feat: audio/video AI/C2PA metadata stripping (MP4/MOV, WAV, MP3) (#139)

The file-cleaners layer covered 15 formats -- all image, document, or
text -- and zero audio/video. That gap gets more expensive every month:
Sora, Veo, ElevenLabs, and Suno all embed provenance through the same
mechanisms image generators do, just in different containers.

New av_meta.py adds inspect/clean for:
- MP4/MOV/M4A/M4V: top-level C2PA (jumb/c2pa box) and XMP (uuid box)
  detection/stripping reuse inspect_isobmff()/strip_isobmff() from
  image_meta.py unchanged -- that's exactly the mechanism the C2PA spec
  defines for ISOBMFF-family containers, already proven for AVIF/HEIC.
  moov/udta (where generator/tool tags live) is handled separately since
  it's MP4-specific.
- WAV: RIFF LIST INFO chunk + embedded id3 chunk.
- MP3: ID3v2 frames, per-frame for v2.3/v2.4, whole-tag fallback for
  v2.2 (3-byte frame IDs are detected but not decomposed, so a partial
  rewrite is never attempted there).

Every box/chunk/frame is either kept byte-identical or dropped whole --
nothing does a partial in-place rewrite of a payload, so a container can
never come out semantically mangled. Default strip_all_metadata=True
matches this project's existing default (privacy-first: drop everything,
--keep-non-ai-metadata narrows to only AI-flagged content), same as the
image cleaners.

Wired through the full dispatch stack so the feature isn't a half
integration: format_dispatch.py (new "av" Kind), inspect_file.py /
clean_file.py (--as av), audit_lib.py (so audit_dir.py's CI/SARIF path
and the pre-commit hooks from #135 both cover audio/video too), and
server.py (HTTP /inspect and /clean).

Closes #134

Co-authored-by: Guillaume Meyer (The Opinionated Man) <1385518+guillaumemeyer@users.noreply.github.com>

README.md

@@ -19,7 +19,7 @@ Agent skill + stdlib Python service to strip **multi-vendor AI provenance marks*
 | --- | --- | --- |
 | **A** | Invisible Unicode, exotic spaces, bidi, tag chars | Deterministic Python scripts |
 | **B** | Statistical (token-sampling) text watermarks | Agent rewrite + optional `rewrite_text.py` hook |
-| **Files** | C2PA / EXIF / XMP / doc props | PNG, JPEG, WebP, BMP, GIF, TIFF, SVG, PDF, DOCX, EPUB, ODT, HTML, Markdown |
+| **Files** | C2PA / EXIF / XMP / doc props | PNG, JPEG, WebP, AVIF, HEIC, BMP, GIF, TIFF, SVG, PDF, DOCX, XLSX, PPTX, EPUB, ODT, HTML, Markdown, MP4/MOV/M4A/M4V, WAV, MP3 |
 
 Vendors / ecosystems (class-level): **Claude**, **Gemini / SynthID-Text**, **OpenAI** provenance surfaces, **open-LLM** Kirchenbauer-style marks.
 
@@ -712,6 +712,9 @@ Layer B makes sense when you specifically want the premium model's **thinking an
 | ODT | meta.xml | Drop generator / AI-ish meta |
 | HTML | meta, JSON-LD, data-ai* | Strip tags/attrs |
 | Markdown | YAML frontmatter AI keys | Drop keys + Layer A body |
+| MP4 / MOV / M4A / M4V | ISOBMFF `jumb`/`uuid` boxes (same mechanism as AVIF/HEIC) + `moov/udta` generator tags | Drop boxes |
+| WAV | RIFF `LIST INFO` chunk, embedded `id3 ` chunk | Drop chunks |
+| MP3 | ID3v2 frames (v2.3/v2.4 per-frame; v2.2 whole-tag) | Drop matched frames or whole tag |
 
 #### Why PDF needs qpdf, not just exiftool