fix(identify): gate C2PA issuer->generator attribution on AI source type (v0.6.5)

Prevents an unmapped C2PA device whose manifest incidentally contains a mapped
issuer substring (e.g. the "Adobe XMP" toolkit string in a Canon/Sony camera
capture) from being mislabeled as that AI generator ("Adobe Firefly").
_attribute_platform now names a specific AI-generator platform only when the
digital-source-type is trainedAlgorithmicMedia; otherwise it degrades to the
neutral "C2PA signer: X" label. Real Firefly/OpenAI/Google output carries the
AI source-type and is unaffected (verified: chatgpt-1.png->OpenAI,
firefly-1.png->Adobe Firefly still attribute). Closes the only real downside of
leaving Canon/Samsung/Bria device signers unmapped: detection and removal were
already unaffected; now the platform label degrades gracefully too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

uv.lock

@@ -2865,7 +2865,7 @@ wheels = [
 
 [[package]]
 name = "remove-ai-watermarks"
-version = "0.6.4"
+version = "0.6.5"
 source = { editable = "." }
 dependencies = [
     { name = "click" },