feat: minimum section duration filter (--min-duration, default 0.5 s)

A single 100 ms RMS window above the noise floor used to become its own
section, so isolated pops (clicks, single raindrops) flooded a day with
thousands of sub-second clips like "21:18 to 21:18". Sections shorter
than min_duration (measured after min_gap merging, so a cluster of blips
spanning longer still flags) are now discarded.

Wired through all coupled places: CLI flag, /api/config, controls-bar
input, /api/analyze query param, and the analysis-cache head keys (old
two-key caches no longer match and are recomputed on next analyse).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -154,6 +154,7 @@ python web.py --dir /path/to/audio         # custom recordings directory
 python web.py --port 8888                  # custom port
 python web.py --margin 15                  # dB above background noise for a section to count as loud (default 12)
 python web.py --min-gap 15                 # grace period in seconds for merging loud sections (default 2)
+python web.py --min-duration 1             # discard loud sections shorter than this many seconds (default 0.5)
 python web.py --analyses-dir /path/to/dir  # where to store analysis cache files (default: <recordings>/analyses)
 ```
 
@@ -164,8 +165,9 @@ Shows recordings grouped by day with collapsible sections. Features:
 - **Day groups** — recordings are grouped under a collapsible day heading showing date, file count, total duration, and total size. The most recent day is expanded by default; older days start collapsed. Expanded state is preserved across filter changes.
 - **Day highlights** — click **★ Highlights** on any day heading to run loudness analysis across all WAV/FLAC files in that day and display a combined activity timeline SVG. Orange segments show when loud sections occurred relative to the day's time span; blue shows the file extents. Labels show the start, midpoint, and end times. When a day has more sections than fit as chips, the chips show the top 50 by score (loudest-above-background first) so the most promising events are reviewed first; J/K still steps through all sections in time order.
 - **Inline playback** — collapsible `▶ Play` button per row; audio loads lazily via a seekable `/stream/` endpoint with HTTP Range support. Metadata is fetched immediately so the duration is visible without pressing play.
-- **Waveform analysis** — on demand per file; computes RMS per 100 ms window and marks sections that stand out above the background. 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** (its peak dB above the floor) used to rank sections by how much they stand out. 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 and min-gap 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.
+- **Waveform analysis** — on demand per file; computes RMS per 100 ms window and marks sections that stand out above the background. 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** (its peak dB above the floor) used to rank sections by how much they stand out. 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. **J** / **K** (or ⏮ / ⏭) step through the queued sections — one file's, or a whole day's after ★ Highlights — and **Auto-advance** plays the next section when one ends, turning a day's detections into a continuous review reel. **⤴ Open in file** 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).
 - **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.
@@ -182,14 +184,14 @@ Everything the UI does goes through these endpoints, so they can also be scripte
 | Endpoint | Description |
 |----------|-------------|
 | `GET /api/files` | File listing with size, mtime, duration, recording state, cached-analysis params |
-| `GET /api/analyze?file=&margin=&min_gap=` | Loud-section analysis: `rms_display` (~800-point waveform), scored `sections`, `duration` |
+| `GET /api/analyze?file=&margin=&min_gap=&min_duration=` | Loud-section analysis: `rms_display` (~800-point waveform), scored `sections`, `duration` |
 | `GET /api/clip?file=&start=&end=` | Section of a WAV/FLAC decoded server-side, returned as a standalone WAV (max 600 s) |
 | `GET /api/cut?file=&start=&end=` | ffmpeg-trimmed copy of the file as a download |
 | `GET /stream/<name>` | Inline playback with HTTP Range support; live files get an on-the-fly patched header |
 | `GET /download/<name>` | Raw file download |
 | `GET /api/status` | Currently recording files (`status.json` passthrough) |
 | `GET /api/storage` | Disk free/total |
-| `GET /api/config` | Server-side defaults for margin and min-gap (seeds the UI controls) |
+| `GET /api/config` | Server-side defaults for margin, min-gap, and min-duration (seeds the UI controls) |
 | `DELETE /api/files/<name>` | Delete a recording and its analysis cache |
 
 Analysis, clips, cut, and delete return `409` for files that are still being recorded.