fix(api,watcher,server): reject moves non-markdown untouched; read caps; BOM; strict routing flag (review of #211, pass 2)

- brain_reject on a parked pdf/txt moves the bytes; it no longer prepends YAML
- raw/ notes are read through a cap (readCapped); an endless reader test fails
  instead of exhausting memory
- a byte-order mark no longer hides a note's wing: key
- INGEST_WING_ROUTING is parsed strictly; a typo stops the server rather than
  leaving routing silently off
- tests for the reserved-wing check in every disguise (Sources, sources., ...)
Mutation-checked.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/api/promote.go

@@ -261,15 +261,19 @@ func RejectNote(brainDir string, opts RejectOptions) (string, error) {
 		return "", fmt.Errorf("a rejected note named %s already exists", filepath.ToSlash(rel))
 	}
 
-	fm, body := parseFrontmatter(string(raw))
-	fm.set("rejected_at", time.Now().UTC().Format(time.RFC3339))
-	if opts.Reason != "" {
-		fm.set("reject_reason", opts.Reason)
-	}
+	content := string(raw)
+	if strings.HasSuffix(base, ".md") {
+		fm, body := parseFrontmatter(string(raw))
+		fm.set("rejected_at", time.Now().UTC().Format(time.RFC3339))
+		if opts.Reason != "" {
+			fm.set("reject_reason", opts.Reason)
+		}
+		content = fm.render() + body
+	} // a pdf or txt is moved byte for byte: prepending frontmatter would alter it
 
 	// Write-then-delete: the source survives any write failure. Both go
 	// through the brain root (hyperguild#188).
-	if err := createBrainFile(brainDir, dest, []byte(fm.render()+body)); err != nil {
+	if err := createBrainFile(brainDir, dest, []byte(content)); err != nil {
 		return "", fmt.Errorf("write rejected note: %w", err)
 	}
 	if err := removeBrainFile(brainDir, src); err != nil {