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/settings-merge.ts

@@ -0,0 +1,25 @@
+// Pure settings helpers extracted from stores/settings.ts so the clamp + the
+// forward-compatible merge (the upgrade path: stored data from an older app
+// version that predates a newer notification category) are unit-testable without
+// pulling in zustand / expo-secure-store.
+
+export function clampPageSize(size: number): number {
+  return Math.max(10, Math.min(200, size))
+}
+
+/**
+ * Merge stored settings over defaults. Stored values win, but any top-level field
+ * or notification category missing from storage falls back to its default — so a
+ * user upgrading to a build with a new setting gets that setting's default rather
+ * than `undefined`. Defaults are passed in to keep this module dependency-free.
+ */
+export function mergeStoredSettings<T extends { notifications: Record<string, boolean> }>(
+  defaults: T,
+  parsed: Partial<T>,
+): T {
+  return {
+    ...defaults,
+    ...parsed,
+    notifications: { ...defaults.notifications, ...parsed.notifications },
+  }
+}