feat(dashboard): move This Week stats into the library bar as a popover

The "This Week" reading-stats strip leaves its full-width row below the
subbar and now lives inside the library bar itself, between the switcher
and the customize/refresh actions. Expanding it opens an absolutely
positioned popover that FLOATS over the collections — opening the stats
no longer shifts the page down.

- LibrarySwitcher gains an optional `center` component slot rendered
  between the left group and the actions group (nil = unused). Series
  and collections call sites pass nil and render byte-identical output.
- DashboardWeekWidget redesigned for the slot: compact inline summary
  (icon, "This Week", minutes; pages/sessions/books/streak reveal at
  md/lg/xl) and a card popover panel with the labeled grid, sync note,
  and the Full stats link moved in from the old summary row.
- Panel anchoring is responsive: below `sm` it anchors to the sticky
  bar itself (details goes static; bar-anchored left-4/right-4, i.e.
  screen-centered); at `sm`+ the details is relative again and the
  panel centers on the widget (w-[30rem], translate-x centering).
- On phones the summary collapses to the chart icon + chevron (bar row
  width is scarce); "This Week"/minutes reveal at `sm`, and the
  "Your Library" title hides below `sm` to keep the row from
  overlapping. Icon-only toggle carries an aria-label.
- web/src/dashboard.ts: click-outside and Escape close the popover,
  re-querying #week-widget per event because htmx replaces it on
  library switches. Rendering untouched (behavior-only island).
- id="week-widget" and all htmx wiring unchanged: week-refresh refetch
  + the /dashboard/week-widget fragment still drive library-scoped
  refreshes behind the switch fade; stats-off suppression now yields an
  empty slot via weekWidgetComponent instead of a hidden strip.
- web/static/style.css rebuilt for the new utilities.

Known behavior (unchanged or deliberate): the bar is sticky, so stats
stay visible while scrolling; a library switch re-renders the details
closed; scopes with no current-week reading show zeros (e.g. Manga).

templates/library_switcher.templ

@@ -1,6 +1,13 @@
 package templates
 
-templ LibrarySwitcher(libData []LibraryData, currentLibraryID string, title string, actions ...templ.Component) {
+// LibrarySwitcher renders the sticky subbar: title + library select on
+// the left (title hidden below `sm` — phones need the row width for the
+// select + actions + the dashboard's stats widget), optional action
+// buttons on the right. `center` is an
+// optional slot between them (nil = unused) — the dashboard passes its
+// "This Week" stats widget here so it participates in the bar's
+// justify-between layout as the middle group.
+templ LibrarySwitcher(libData []LibraryData, currentLibraryID string, title string, center templ.Component, actions ...templ.Component) {
 	<div
 		class="app-subbar backdrop-blur border-b"
 		style="background-color: color-mix(in srgb, var(--bg-primary) 88%, transparent); border-color: color-mix(in srgb, var(--text-primary) 6%, transparent);"
@@ -8,7 +15,7 @@ templ LibrarySwitcher(libData []LibraryData, currentLibraryID string, title stri
 		<div class="w-full px-4 sm:px-6 lg:px-8 py-3 flex items-center justify-between gap-4">
 			<div class="flex items-center gap-3 min-w-0">
 				if title != "" {
-					<span class="text-base font-bold tracking-tight shrink-0" style="color: var(--text-primary)">{ title }</span>
+					<span class="text-base font-bold tracking-tight shrink-0 hidden sm:inline" style="color: var(--text-primary)">{ title }</span>
 				} else {
 					<label class="text-sm font-medium" style="color: var(--text-secondary)">Library</label>
 				}
@@ -33,6 +40,9 @@ templ LibrarySwitcher(libData []LibraryData, currentLibraryID string, title stri
 				}
 				</select>
 			</div>
+			if center != nil {
+				@center
+			}
 			if len(actions) > 0 {
 				<div class="flex items-center gap-2">
 					for _, action := range actions {