fix(api): propagate note to Gemini virtual auths and align priority parsing

- Read note from Attributes (consistent with priority) in buildAuthFileEntry,
  fixing missing note on Gemini multi-project virtual auth cards.
- Propagate note from primary to virtual auths in SynthesizeGeminiVirtualAuths,
  mirroring existing priority propagation.
- Sync note/priority writes to both Metadata and Attributes in PatchAuthFileFields,
  with refactored nil-check to reduce duplication (review feedback).
- Validate priority type in fallback disk-read path instead of coercing all values
  to 0 via gjson.Int(), aligning with the auth-manager code path.
- Add regression tests for note synthesis, virtual-auth note propagation, and
  end-to-end multi-project Gemini note inheritance.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/watcher/synthesizer/file.go

@@ -229,6 +229,10 @@ func SynthesizeGeminiVirtualAuths(primary *coreauth.Auth, metadata map[string]an
 		if priorityVal, hasPriority := primary.Attributes["priority"]; hasPriority && priorityVal != "" {
 			attrs["priority"] = priorityVal
 		}
+		// Propagate note from primary auth to virtual auths
+		if noteVal, hasNote := primary.Attributes["note"]; hasNote && noteVal != "" {
+			attrs["note"] = noteVal
+		}
 		metadataCopy := map[string]any{
 			"email":             email,
 			"project_id":        projectID,