Ship the measured Meta Content Seal cohort with auto routing and --vendor override

Full Meta Muse Image support in the invisible-removal path:

- QWEN_ZIMAGE_META_STRENGTH = 0.1: derived by the standard
  worst-boundary-plus-cross-source-spread method over five oracle-bracketed
  generations (data/contentseal/manifest.csv)
- Auto mode: vendor_for_strength routes a file whose only provenance is the
  standalone AI IPTC trainedAlgorithmicMedia tag onto the meta cohort; C2PA
  issuers win first, so Google/OpenAI/Microsoft routing is unchanged. Muse
  WebP outputs place the XMP in a tail chunk, so the scan uses the shared
  chunk-aware metadata.scan_head rather than a plain head read
- Explicit override: --vendor on invisible/all/batch and
  InvisibleOptions.vendor name the cohort on stripped files; naming a cohort
  asserts the watermark is present, so the no-signal gate treats it like
  --force at both the CLI and API seams
- sdxl-zimage has no measured Meta rung: an explicit meta vendor falls to
  the conservative unknown 0.25 rather than inventing one
- identify emits a Content Seal caveat pointing at the removal path
- The legacy visible 'Imagined with AI' mark stays unregistered: a dedicated
  sample hunt (newsroom mockups, community posts, press screenshots, dead
  imagine.meta.com, broken Wayback captures) found no pixel-verifiable
  capture, and the registry rule forbids encoding a corner without one.
  erase --region remains its removal path; outcome recorded in the landscape

Co-Authored-By: Claude Fable 4.5 <noreply@anthropic.com>

docs/python-api.md

@@ -112,6 +112,18 @@ raiw.remove_all(
 )
 ```
 
+`vendor="meta"` names a strength cohort explicitly (the measured Content Seal
+floor) for a stripped file whose provenance no longer carries the AI IPTC tag,
+and implies the scrub runs:
+
+```python
+raiw.remove_all(
+    "muse_output.webp",
+    "clean.png",
+    invisible=InvisibleOptions(vendor="meta"),
+)
+```
+
 `InvisibleOptions` carries only what `InvisibleEngine` itself takes, and uses the
 engine's own parameter names and defaults. `force`, which decides whether the
 engine runs at all, is a parameter of `remove_all` and `remove_batch` alongside