fix(brain): move the wikilink strip into WriteNote/UpdateNote

The BrainStore is not the only door. POST /write — the HTTP path CLAUDE.md
hands to curl and scripts — calls api.WriteNote directly, so the strip
shipped one commit ago covered brain_write and capture while leaving the raw
door ungated. A gate one door wide is not a gate.

The BrainStore keeps its own call so it can still report Ref.Unlinked to the
MCP caller; running the strip twice is a no-op on content the primitive has
already cleaned.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ingestion/internal/api/handler.go

@@ -133,6 +133,16 @@ func WriteNote(brainDir string, opts WriteNoteOptions) (string, error) {
 		return "", fmt.Errorf("content is required")
 	}
 
+	// In the primitive, not in a caller: POST /write reaches here directly,
+	// without the BrainStore, and a gate one door wide is not a gate.
+	// BrainStore still calls the strip itself to report Ref.Unlinked; the
+	// second pass is a no-op on already-clean content.
+	clean, _, err := brain.StripUnresolvedLinks(brainDir, opts.Content)
+	if err != nil {
+		return "", err
+	}
+	opts.Content = clean
+
 	if opts.Wing != "" && opts.Hall != "" {
 		return writeHallNote(brainDir, opts)
 	}