Implement share viewer (task 31)

- Makes actorId nullable in activity_log (migration 0010) with onDelete:
  set null so audit history survives user deletion; adds logShareActivity
  for anonymous mutations
- Adds resolveShareToken return of householdId for downstream validation
- Adds renderSharedView to EntityTypeRegistration; each module implements
  loadForShare (no-session bare queries) and renderSharedView
- Calendar: CalendarSharedView (upcoming 90-day events) and
  EventSharedView (title/time/location/notes)
- Lists: ListSharedView (client component with optimistic toggles via
  toggleShareListItem server action in lists/server/share-actions.ts)
- Notes: NoteSharedView (title + body + updated date)
- /app/s/[token]/page.tsx: resolves token, dispatches to loadForShare +
  renderSharedView, friendly error for invalid/expired tokens, noindex
- Middleware /s/* exemption confirmed present (no change needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/_core/activity.ts

@@ -18,3 +18,20 @@ export async function logActivity(input: {
     payload: input.payload ?? null,
   });
 }
+
+export async function logShareActivity(input: {
+  householdId: string;
+  entityType: string;
+  entityId: string;
+  action: string;
+  payload?: Record<string, unknown>;
+}): Promise<void> {
+  await db.insert(activityLog).values({
+    householdId: input.householdId,
+    entityType: input.entityType,
+    entityId: input.entityId,
+    actorId: null,
+    action: input.action,
+    payload: input.payload ?? null,
+  });
+}