refactor: split web.py — detector and audio-format helpers into isrweb/

Pure move, no behaviour change. web.py 1221 -> 807 lines.

The reason is not file size but isolation of change. CLAUDE.md records
that the next step for detection, should flagging ever need improving, is
a spectral filter or an optional Silero VAD over candidate sections —
that work now lands entirely in isrweb/loudness.py and never has to open
the HTTP layer. The byte-level format code (FLAC frame parsing, CRC-8,
live header patching) is a second self-contained cluster, touched only
when a container format misbehaves.

  isrweb/loudness.py   229  detector + its tuning constants
  isrweb/audiofile.py  250  filename clock, WAV/FLAC headers, MIME types
  web.py               807  cache, listing, handler, main()

Import direction is strictly web.py -> {loudness, audiofile}; the two
leaves import neither each other nor web.py, which is what lets the
detector be imported and tested without an HTTP server.

A package rather than flat modules because `audiofile` is a real PyPI
name and `detect` is generic enough to collide; a local file silently
shadows an installed one, which fails confusingly rather than loudly.
web.py stays at the repo root so `python web.py`, the docker-compose
command and the webui.html lookup are all unchanged.

Each module keeps its own optional numpy/soundfile try-import rather than
sharing one. That block cannot meaningfully diverge — if numpy is
installed every copy says True — and sharing it would stop isr.py being a
standalone file you can drop on a Pi and run.

Tests mirror the modules: test_loudness.py, test_audiofile.py, test_web.py
(+ unchanged test_isr.py). New tests/conftest.py owns the sys.path setup
that was previously an inline hack in test_isr.py — which only worked for
the other modules because that file happened to import first — and
provides the write_wav fixture the split would otherwise have duplicated.

Verified:
* 78 passed, same count as before the split; each test file also passes
  standalone.
* All 21 moved functions diffed against HEAD:web.py — byte-identical.
* Import graph asserted acyclic; both leaves import with `web` absent
  from sys.modules.
* An analysis cache written *before* the split still hits afterwards,
  with identical sections — the one way a "pure" move could quietly
  invalidate every user's cache.
* Endpoint smoke (analyze bounds, cache hit, cached_analysis in the
  listing, clip Content-Length, 8-bit rejection) and the byte-serving
  harness (ranges, download Range, HEAD, 405, live-header patching whole
  and straddling) both re-run green.
* Dockerfile COPY set verified by building the image's file tree in a
  temp dir and importing web.py with nothing else present.

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

CLAUDE.md

@@ -5,14 +5,16 @@ Guidance for Claude Code when working in this repository.
 ## Rules
 
 - **Always update `README.md`** when user-facing behaviour changes (flags, endpoints, Docker setup, features), and **commit it in the same commit** as the code change. README is the external reference; CLAUDE.md documents internals.
-- Run `python -m pytest tests/` after changing `isr.py` or `web.py` (tests cover the recorder and the loud-section detector).
+- Run `python -m pytest tests/` after changing `isr.py`, `web.py` or `isrweb/` (tests cover the recorder, the detector, the filename clock and the HTTP layer). Test files mirror the modules: `test_isr.py`, `test_loudness.py`, `test_audiofile.py`, `test_web.py`; `tests/conftest.py` owns the sys.path setup and the `write_wav` fixture.
 
 ## Files
 
 | File | Purpose |
 |------|---------|
 | `isr.py` | Recorder: streams (Icecast/HTTP) + ALSA soundcards, time-aligned file splits |
-| `web.py` | Archive browser: HTTP server, file listing, RMS loudness analysis, cut/delete |
+| `web.py` | Archive browser: HTTP server, file listing, analysis cache, cut/delete. Entry point — stays at the repo root so `python web.py` and the `webui.html` lookup work |
+| `isrweb/loudness.py` | The adaptive loud-section detector. Pure computation, imports nothing from the app — future spectral/VAD work lands here and never touches HTTP |
+| `isrweb/audiofile.py` | What an audio file is and what its name means: the filename clock, FLAC/WAV header parsing, live-header patching. Also a leaf |
 | `webui.html` | Single-page UI (HTML/CSS/JS), loaded by `web.py` at startup — must sit next to `web.py` and be copied in the Dockerfile |
 | `config.ini` | Recording sources; copy from `config.example.ini`. `[general]` gives defaults, every other section is a source (`type = stream` or `type = soundcard`) |
 | `asound.conf` | dsnoop device `shared_mic` so ISR and other ALSA apps can share a soundcard |
@@ -30,11 +32,17 @@ Dependencies: `requests` (streams), `numpy` + `soundfile` (FLAC output and FLAC
 
 ## Code map
 
-`web.py`:
+**Import direction is strictly `web.py → {isrweb.loudness, isrweb.audiofile}`.** The two leaves never import each other or `web.py`; keep it that way, it is what lets the detector be tested without an HTTP server. Each module carries its own optional numpy/soundfile try-import — that boilerplate cannot meaningfully diverge, and sharing it would stop `isr.py` being a standalone file.
+
+`isrweb/loudness.py`:
 - Detection: `_compute_rms_windows_wav()` / `analyze_flac()` produce 100 ms RMS windows (at 48 kHz — `WINDOW_SAMPLES` is a fixed sample count, so windows are wider on lower-rate files; `analyze_wav()` rejects anything that is not 16-bit, which the RMS decoder assumes) → `_noise_floor_db()` estimates the rolling floor → `_loud_sections()` emits scored sections → `_package_result()` shapes the `/api/analyze` payload.
-- Clips: `_api_clip()` validates params, `_clip_wav()` / `_clip_flac()` stream the decoded slice, `_wav_header()` builds the 44-byte PCM header.
+
+`isrweb/audiofile.py`:
 - Filenames as a clock: `_recording_start()` parses the start time out of a filename stem; `_cut_filename()` turns a (stem, ext, start, end) into a wall-clock-named cut. Both the listing `date` field and `_api_cut()` use them.
-- Live headers: `_live_wav_header()`, `_live_flac_header()` (+ `_flac_frame_samples()`, CRC-8 verified).
+- Live headers: `_live_wav_header()`, `_live_flac_header()` (+ `_flac_frame_samples()`, CRC-8 verified). Plus `_wav_header()` (44-byte PCM header for clips), `_get_audio_duration()`, `MIME_TYPES`, `AUDIO_EXTENSIONS`.
+
+`web.py`:
+- Clips: `_api_clip()` validates params, `_clip_wav()` / `_clip_flac()` stream the decoded slice.
 - Serving: `_serve_bytes()` is the single Range-capable file sender — `_stream()` (live header patch via its `prefix` argument, `no_store`) and `_download()` (`Content-Disposition`) both go through it, and it is what makes `do_HEAD` a body-less `do_GET`. Plus `_copy_to_response()`, `_safe_path()` (path traversal guard).
 
 `webui.html` (one `<script>` block):