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/schema.ts

@@ -97,8 +97,7 @@ export const activityLog = pgTable(
     entityType: text("entity_type").notNull(),
     entityId: uuid("entity_id").notNull(),
     actorId: uuid("actor_id")
-      .notNull()
-      .references(() => users.id, { onDelete: "cascade" }),
+      .references(() => users.id, { onDelete: "set null" }),
     action: text("action").notNull(),
     payload: jsonb("payload").$type<Record<string, unknown> | null>(),
     createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),