feat: loudness walk (U/I) keeps its own cursor, independent of J/K

The clip bar had one shared cursor, so pressing U/I re-derived the
loudness rank from wherever you currently were. A J/K detour to review
clips around an interesting spot therefore hijacked the loudness walk:
returning to U/I continued from the J/K position, not from where the
ranking left off.

Add a separate scoreCursor that only U/I (and "highlights only" auto-
advance) move; J/K never touches it. So: U/I to a loud moment, J/K to
review the time-adjacent clips, U/I again resumes the ranking exactly
where you left it. scoreCursor resets to -1 on every explicit jump /
queue re-arm (hideClipBar, chip clicks, day-highlights arm) so the next
U/I re-anchors on the selected section.

Also label the position count "by time" (J/K) or "by loudness" (U/I) so
the blind user can hear which dimension the count is in — the two looked
identical before and switched meaning silently when changing keys.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -159,7 +159,7 @@ Shows recordings grouped by day with collapsible sections. Features:
 - **Loudness analysis** — on demand per file; computes RMS per 100 ms window and lists sections that stand out above the background as clickable chips (no visual waveform — the UI is built for screen-reader use). Detection is **adaptive**: a rolling noise floor (20th percentile per 30 s block) is estimated across the file, and a section is flagged when the level rises at least *margin* dB (default 12) above that floor. Slow ambience changes — rain setting in, day/night traffic hum — move the floor instead of producing false positives. Each section gets a **score** used to rank it: its peak dB above the floor, capped by the sharpest rise within 0.5 s. Abrupt events — voices, impacts, barks — rise fast, so their score is their full prominence; a gradual swell (a gust, a distant approaching car) that drifts up faster than the floor can track still gets flagged, but scores near zero and sinks to the bottom of the highlight ranking. Supported for WAV and FLAC (FLAC requires `numpy` + `soundfile`). Pure-Python fallback for WAV when numpy is absent. Results are cached in `recordings/analyses/<filename>.analysis.json`; subsequent requests at the same margin, min-gap, and min-duration settings return instantly without re-reading the audio. The cache file is deleted automatically when the audio file is deleted. Orphaned cache files (audio deleted outside the UI) are pruned on startup.
 - **Grace period** — configurable in the controls bar (default 2 s). Loud sections separated by less than this gap are merged into one. Raise this (e.g. to 15–30 s) when a single event generates many timestamps due to brief quiet gaps within it.
 - **Min duration** — configurable in the controls bar (default 0.5 s). Loud sections shorter than this (after grace-period merging) are discarded, so isolated sub-second pops — a click, a single raindrop — don't flood a day with thousands of near-zero-length sections. Set to 0 to disable.
-- **Clip playback** — clicking a loud-section chip plays a short server-rendered WAV clip (`/api/clip`, pre-roll included) in a player bar at the bottom of the page. Playback starts instantly even for sections deep inside multi-hundred-MB FLACs, because the browser never has to seek the full file. The player bar labels each clip with the wall-clock time it occurred (derived from the recording's filename), its loudness above the background, and its position in the queue, e.g. `17:09:56 to 17:09:57 · +30 dB (30 / 426)` — and the exact same text is announced to screen readers, so the spoken and visible labels never differ. The filename and in-file offset are in the label's hover tooltip. **J** / **K** (or the **Prev** / **Next** buttons) always step through the queued sections in time order — one file's, or a whole day's after **Highlights** — and the position count is then the chronological index (e.g. `30 / 426` is the 30th section in time). **U** / **I** step through the same queue by loudness instead: **I** plays the next-loudest section, **U** goes back up the ranking, and the count becomes the rank in that loudness order (`1 / 426` is the loudest of all reachable sections, `2 / 426` the next-loudest, and so on) — the denominator stays the full count because U/I reaches every section, with no top-N cutoff; the chip list shown on screen is capped only for display. So a day with thousands of detections is reviewed loudest-first for as long as it stays interesting — just stop when it gets boring. Both key pairs drive one shared queue and one cursor, so you can mix them: find a loud moment with **U** / **I**, then press **J** / **K** to review the clips immediately before and after it in time (the count switches from rank back to the chronological index as you do). The auto-advance radio in the player bar picks what happens when a clip ends: **Don't auto-advance**, **Auto-advance** (next section in time), or **Auto-advance highlights only** (next section by loudness) — it never changes what J/K do. Holding **Shift** with any of these jumps to the extreme in that direction — **Shift+J**/**Shift+K** to the first/last section in time, **Shift+U**/**Shift+I** to the loudest/quietest. The same keys work during full-file playback, seeking the open recording to the next section in time (J/K) or by loudness (U/I). **Open in file** (or the **O** key) switches to the full recording at the same position for context; each chip click also pre-fills the cut panel.
+- **Clip playback** — clicking a loud-section chip plays a short server-rendered WAV clip (`/api/clip`, pre-roll included) in a player bar at the bottom of the page. Playback starts instantly even for sections deep inside multi-hundred-MB FLACs, because the browser never has to seek the full file. The player bar labels each clip with the wall-clock time it occurred (derived from the recording's filename), its loudness above the background, and its position in the queue, e.g. `17:09:56 to 17:09:57 · +30 dB (30 / 426 by time)` — and the exact same text is announced to screen readers, so the spoken and visible labels never differ. The filename and in-file offset are in the label's hover tooltip. **J** / **K** (or the **Prev** / **Next** buttons) always step through the queued sections in time order — one file's, or a whole day's after **Highlights** — and the count is then the chronological index, labelled **by time** (e.g. `30 / 426 by time` is the 30th section in time). **U** / **I** step through the same queue by loudness instead: **I** plays the next-loudest section, **U** goes back up the ranking, and the count becomes the rank in that loudness order, labelled **by loudness** (`1 / 426 by loudness` is the loudest of all reachable sections, `2 / 426 by loudness` the next-loudest, and so on) — the denominator stays the full count because U/I reaches every section, with no top-N cutoff; the chip list shown on screen is capped only for display. So a day with thousands of detections is reviewed loudest-first for as long as it stays interesting — just stop when it gets boring. The loudness walk keeps its own position **independently** of J/K: find a loud moment with **U** / **I**, press **J** / **K** to review the clips immediately before and after it in time, and pressing **U** / **I** again resumes the loudness ranking exactly where you left it — the J/K detour never moves your place in the loudest-first walk. (Clicking a chip is an explicit jump, so it re-anchors the next U / I there.) The auto-advance radio in the player bar picks what happens when a clip ends: **Don't auto-advance**, **Auto-advance** (next section in time), or **Auto-advance highlights only** (next section by loudness) — it never changes what J/K do. Holding **Shift** with any of these jumps to the extreme in that direction — **Shift+J**/**Shift+K** to the first/last section in time, **Shift+U**/**Shift+I** to the loudest/quietest. The same keys work during full-file playback, seeking the open recording to the next section in time (J/K) or by loudness (U/I). **Open in file** (or the **O** key) switches to the full recording at the same position for context; each chip click also pre-fills the cut panel.
 - **Cut & download** — `Cut` button opens the player row and reveals a cut panel. Enter start and end times in `m:ss` or `h:mm:ss` format and click **Download cut** to receive an ffmpeg-trimmed copy without re-encoding. Requires ffmpeg (included in the Docker image). The cut is named with the real wall-clock span it covers — `<YYYYMMDD>_<HH-MM-SS>_<HH-MM-SS>.<ext>`, e.g. a 22:31:30→22:32:30 slice of a recording started at 22:00:00 becomes `20260523_22-31-30_22-32-30.flac`.
 - **Filters** — live filename search and from/to date pickers above the table; applied client-side with no additional requests. Shows `N of M shown` when a filter is active.
 - **Delete** — `Delete` button per row with confirmation prompt; disabled for files currently being recorded; sends `DELETE /api/files/<name>` and re-renders the table.