test(stores): cover settings merge/clamp + notification sanitizer (29→42 tests)

Extract two pure helpers so they're testable without zustand/expo:
- settings-merge.ts: clampPageSize + forward-compatible mergeStoredSettings (the
  upgrade path where stored data predates a new notification category must yield
  the default, not undefined). stores/settings.ts now delegates.
- notify-format.ts: sanitizeBody (strip C0/DEL control chars, trim, cap at 200)
  used for server-supplied notification text. stores/events.ts now imports it.
Behavior unchanged; typecheck clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/notify-format.ts

@@ -0,0 +1,14 @@
+// Pure formatting for notification bodies, extracted from stores/events.ts so the
+// sanitization rules are unit-testable without the event store's RN dependencies.
+
+export const MAX_NOTIF_BODY = 200
+
+/**
+ * Make a server-supplied string safe to show in a notification:
+ * strip C0 control characters and DEL (which can corrupt the notification shade
+ * or hide content), collapse surrounding whitespace, and cap the length. Falls
+ * back to `fallback` when the input is empty/whitespace-only or undefined.
+ */
+export function sanitizeBody(s: string | undefined, fallback: string): string {
+  return (s ? s.replace(/[\x00-\x1f\x7f]/g, " ").trim().slice(0, MAX_NOTIF_BODY) : "") || fallback
+}