feat(dashboard): collapsible This Week widget, library-scoped + switch-surviving; title into the subbar

Three dashboard complaints, one build:

- The widget collapses to a single summary row (This Week · minutes ·
  pages · sessions · books · streak · Full stats) on every screen size
  and expands to the full grid via a details/summary toggle — the
  carousel sections start immediately below it again.
- The 'Your Library' heading moved into the library switcher subbar
  (LibrarySwitcher gains an optional title param; collections/series
  keep the plain 'Library' label). The standalone heading block is
  gone.
- Root-caused the JS-switch vanishing: renderDashboardCollections
  replaces ALL of #collections-container's innerHTML, so anything
  server-rendered inside it (title, widget) died on the first library
  switch. The widget now re-fetches ITSELF: a /dashboard/week-widget
  fragment (same resolveLibrary family-lens rules as the page) is
  pulled by htmx whenever the switcher dispatches week-refresh —
  carrying the current #library-select value — so the widget both
  survives switches and RE-SCOPES to the switched library. Initial SSR
  renders the same scope the sections use.

ThisWeek (and the streak calendar) gained an optional library filter.
Tests: TestReadingStatsWeekLibraryScope — per-library totals, scoped
streaks, invisible-library isolation, malformed id 400. Full suite
PASS.

internal/database/queries/queries.sql

@@ -1486,6 +1486,7 @@ JOIN media_items mi ON mi.id = rh.media_item_id
 WHERE rh.user_id = sqlc.arg('user_id')
   AND COALESCE(rh.reading_session_end, rh.created_at) >= sqlc.arg('start_time')
   AND COALESCE(rh.reading_session_end, rh.created_at) <= sqlc.arg('end_time')
+  AND (sqlc.narg('library_id')::uuid IS NULL OR mi.library_id = sqlc.narg('library_id')::uuid)
   AND (sqlc.narg('visible_library_ids')::uuid[] IS NULL OR mi.library_id = ANY(sqlc.narg('visible_library_ids')::uuid[]))
 ORDER BY rh.created_at ASC;
 
@@ -1551,6 +1552,7 @@ FROM reading_history rh
 JOIN media_items mi ON mi.id = rh.media_item_id
 WHERE rh.user_id = sqlc.arg('user_id')
   AND COALESCE(rh.reading_session_end, rh.created_at) >= sqlc.arg('start_time')
+  AND (sqlc.narg('library_id')::uuid IS NULL OR mi.library_id = sqlc.narg('library_id')::uuid)
   AND (sqlc.narg('visible_library_ids')::uuid[] IS NULL OR mi.library_id = ANY(sqlc.narg('visible_library_ids')::uuid[]))
 ORDER BY day ASC;