feat: day-grouped table, day highlights timeline, and grace period for loud sections

- Recordings table now groups files by day with collapsible headings
  showing file count, total duration, and size; most recent day expands
  by default, older days start collapsed
- Day highlights button runs loudness analysis across all WAV/FLAC files
  in a day and renders a combined SVG activity timeline (blue = file
  extents, orange = loud sections) with time labels
- Grace period control (default 2 s, max 300 s) merges loud sections
  separated by less than this gap; exposed in the controls bar, via
  --min-gap CLI flag, and as a per-request min_gap param on /api/analyze
- Delete re-renders via applyFilters so day headings stay consistent

README.md

@@ -151,16 +151,20 @@ python web.py                        # serves ./recordings on port 8080
 python web.py --dir /path/to/audio   # custom recordings directory
 python web.py --port 8888            # custom port
 python web.py --threshold 0.03       # loudness threshold 0–1 (default 0.05)
+python web.py --min-gap 15           # grace period in seconds for merging loud sections (default 2)
 ```
 
-Shows a table of all recordings sorted newest-first. Features:
+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.
 - **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 highlights loud sections. Supported for WAV and FLAC (FLAC requires `numpy` + `soundfile`). Pure-Python fallback for WAV when numpy is absent.
+- **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.
 - **Timestamp jump** — after analysis, click any loud-section chip to seek the player to that position and pre-fill the cut panel. Use **J** / **K** keyboard shortcuts to jump to the previous / next section while audio is playing.
 - **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.
-- **Delete** — `✕ Delete` button per row with confirmation prompt; disabled for files currently being recorded; sends `DELETE /api/files/<name>` and removes the row without a full page reload.
+- **Delete** — `✕ Delete` button per row with confirmation prompt; disabled for files currently being recorded; sends `DELETE /api/files/<name>` and re-renders the table.
 - **Live REC badge** — files currently being written by `isr.py` show an animated REC indicator, polled every 5 seconds via `/api/status`. Duration for in-progress files shows `—` (header is unfinalized until recording stops).
 - **WCAG-compliant** — skip link, `aria-expanded`/`aria-controls` on the player toggle, `aria-live` status, focus management, `role=img` on SVG waveforms.