fix(claudewatcher): tag session-dump notes source_type: internal

brain-gardener#5: the audit's unsourced check was flagging 59 raw
claudewatcher session dumps as high-severity hallucination risk,
because it can't distinguish a first-party observation (a session
transcript) from an external claim needing citation.

Adds WriteNoteOptions.SourceType, emitted as source_type: <value> in
the wing/hall frontmatter route. claudeSink (the claudewatcher sink)
now always sets source_type: internal on the notes it writes.

ingestion/cmd/server/main.go

@@ -68,12 +68,13 @@ func (s *claudeSink) Ingest(ctx context.Context, b claudewatcher.Batch) error {
 	}
 	slug := "session-" + b.Host + "-" + b.SessionID
 	if _, err := api.WriteNote(s.brainDir, api.WriteNoteOptions{
-		Filename: slug,
-		Wing:     "claude-sessions",
-		Hall:     "facts",
-		Type:     "source",
-		Domain:   b.ProjectID,
-		Content:  sb.String(),
+		Filename:   slug,
+		Wing:       "claude-sessions",
+		Hall:       "facts",
+		Type:       "source",
+		Domain:     b.ProjectID,
+		Content:    sb.String(),
+		SourceType: "internal", // raw session transcript, not an external claim (brain-gardener#5)
 	}); err != nil {
 		return fmt.Errorf("write claude session note: %w", err)
 	}