feat(reader): fullscreen mode; revert stacked volume; fix manga badges + ghost sidebar

Reader fullscreen: the topbar gains a fullscreen toggle (icon state + f
shortcut + help row; f is guarded so Ctrl/Cmd+F stays find-in-page).
Enter requests the Fullscreen API with fallbacks (desktop/Android get a
true full display; iOS Safari has no page-fullscreen API and falls back
to the soft visual mode only). Margins: the foliate paginator's closed
shadow root only yields through its observed 'margin' attribute, so
fullscreen fits a comfortable ratio (6% of the short side, floored at
48px) and floors it by the measured env insets — Android reports true
cutout insets in fullscreen, so portrait phones keep text clear of the
camera band; iOS letterboxes are already env-padded chrome. Fixed-layout
renderers skip it (fxl/webtoon pack pages edge-to-edge by design).
Exits the user makes outside the toggle (Esc, browser UI) sync via
fullscreenchange(+webkit) and restore the ordinary 48px margin; a
position-keeping re-render follows the ResizeObserver re-entry path.
Verified on-device: enter -> true fullscreen + icon swap + camera band
clear, exit -> chrome back, margins restored, position kept.

Volume: revert the stacked panel — the popup returns to the liked shape
(mute button left, horizontal dragger right, dialogue above the strip);
one-line flex restore of the pre-89665fb layout.

Manga badges: MediaBadgeKind makes the library type authoritative for
the comic/manga split — manga volumes ship as fixed_layout scans as
often as comic_archive (and manga_type is unreliable across sources:
unknown/NULL on real rows), so the old comic_archive+manga mapping left
the scan volumes unbadged. Anything in a manga library reads manga;
anything in a comics library reads comic. Verified: /dashboard lands 24
title="Manga" cover badges for the Manga library and the sections API
reports badge=manga for a fixed_layout item.

Ghost sidebar: the >=1024px media block applied body
padding-left:var(--sidebar-w) unconditionally, so pages that never
render the sidebar (logged-out pages, the audio player, the reader
itself) carried a phantom 16rem left margin that pushed content off
center on desktop widths. The body:has(.app-sidebar) rule below was
already the correct conditional source — it is now the only one.
Verified in the built stylesheet: exactly one such rule remains.

Infra: main.js ?v=3 stamp bump (reader.ts changed; hashed chunks churn
their URLs themselves).

templates/header.templ

@@ -213,7 +213,7 @@ templ Header(user User, currentPath string) {
 		</header>
 		<!-- module bundle; ?v=<commit-ish stamp> busts stale intermediate
 		     builds across app restarts (browser caches are keyed by URL) -->
-		<script type="module" src="/static/main.js?v=2c714dc"></script>
+		<script type="module" src="/static/main.js?v=3"></script>
 	</div>
 }