Stop double-counting a named forensic mark as SynthID provenance

A manifest that names its own forensic soft-binding algorithm carries
that vendor's mark; the generic watermark-action vendor-token inference
must not add a second, differently-attributed invisible watermark from
the same bytes. Microsoft Designer manifests triggered exactly that:
signed by Microsoft, watermarked by InvisMark, with the generation
agent named "Azure OpenAI ImageGen" - the OpenAI issuer token inside
that service name plus the InvisMark watermarked action satisfied the
OpenAI SynthID-evidence rule, and identify reported one forensic mark
as two paid pixel watermarks.

Three changes, one rule at every inference site (the verdict-scan
comment's own lesson: a rule that lives in only one copy is a rule the
others silently lack):

- c2pa.py structured path: SynthID evidence now scopes to the
  signer/generator identity strings only (signature issuer, claim
  generator), never the raw chain, and is suppressed entirely when a
  soft-binding algorithm is named.
- c2pa.py byte fallback and metadata.py synthid_source: suppressed when
  the scan names a soft-binding algorithm.
- identify.py verdict scan: same suppression.

Gemini and ChatGPT originals keep their provenance-asserted SynthID
strings; the Designer regression is pinned by
test_designer_synthid_suppression.py (agent name alone is not the
vendor's provenance, and a named soft binding suppresses the
inference).

pyproject.toml

@@ -4,7 +4,7 @@
 # on it, including the ComfyUI node package. The console script below carries
 # the same weight, since users have it on PATH.
 name = "remove-ai-watermarks"
-version = "0.32.0"
+version = "0.32.1"
 description = "AI watermark remover for visible, invisible, and provenance marks in images and video"
 readme = "README.md"
 requires-python = ">=3.11,<3.15"