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>

src/remove_ai_watermarks/api.py

@@ -232,6 +232,7 @@ class InvisibleOptions:
 
     strength: float | None = None
     pipeline: str = "qwen-zimage"
+    vendor: str | None = None
     seed: int | None = None
     hf_token: str | None = None
     humanize: float = 0.0
@@ -487,13 +488,17 @@ def _run_invisible(
     if not is_available():
         say("invisible", "unavailable")
         return "unavailable"
-    if not (force or evidence.has_invisible_target()):
+    if not (force or opts.vendor is not None or evidence.has_invisible_target()):
         say("invisible", "no-signal")
         return "no-signal"
 
     from remove_ai_watermarks._internal.watermark_profiles import resolve_strength, vendor_for_strength
 
-    vendor = vendor_for_strength(vendor_source)
+    # An explicit vendor override wins over detection and implies the scrub runs:
+    # naming the cohort (e.g. "meta" for Muse Image Content Seal, which carries no
+    # provenance to detect) asserts the pixel watermark is present, so the no-signal
+    # gate must not skip it.
+    vendor = opts.vendor or vendor_for_strength(vendor_source)
     # Report the strength the engine will actually execute, resolved the same way it
     # resolves it, so the reported value cannot drift from the executed one.
     with suppress(Exception):