fix(ui): right slide-out sheet for oversized modals on phones; 360px fixes

Auditing at 360x760 (Firefox's smallest emulated device; Galaxy S25
class) — 390 was too generous a baseline — the Customize Dashboard
pop-up was the worst page in the app: its card measured 986px in a
760px viewport with no internal scroll, so Cancel/Save sat ~90px below
the fold on a fixed, non-scrolling overlay — unreachable.

New reusable shell: .app-modal-panel (input.css) renders a centered
dialog on desktop (>=640px, unchanged) and a full-height right
slide-out sheet on phones: h-dvh, rounded-l-2xl, slide-in animation
(replays on every open because the overlay toggles display), internal
scroll, overscroll containment. Overlay pairs with items-stretch /
justify-end below sm.

Converted the measured overflows:
- Customize Dashboard (986px): sheet + sticky header/footer, rows wrap
  with the Restore/toggle group right-aligned (ml-auto), titles
  truncate, System badge shrink-0.
- Collection create/edit (796px, cut at both ends at 360): sheet +
  sticky header/footer; edit modal shared the file.

Also at 360: admin-library's Archived buttons row (View Archived +
Purge Archived Now, 315px at x=49) inflated the page to 364px — now
flex-wrap. Collection-episodes shows a 1px sub-pixel rounding artifact
(vw=361) — left as-is, invisible.

Verified at 360x760: sheet geometry (footer bottom 739 < 760), rows
fit, desktop 1280 screenshot unchanged; full-route sweep at 360 shows
no page-level horizontal overflow beyond the two notes above.

templates/admin_library_templ.go

@@ -95,7 +95,7 @@ func AdminLibrary(user User, libraries []LibraryData, users []User, archivedCoun
 			if templ_7745c5c3_Err != nil {
 				return templ_7745c5c3_Err
 			}
-			templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 8, "</a></p><p class=\"text-sm\" style=\"color: var(--text-secondary)\">Files missing from disk for two consecutive scans. Reading history is kept unless purged; items return automatically if their files come back.</p></div><div class=\"flex items-center gap-2\"><a href=\"/admin/archived\" class=\"btn btn-secondary\">View Archived</a> <button type=\"button\" @click=\"purgeArchivedItems()\" class=\"btn btn-secondary\">")
+			templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 8, "</a></p><p class=\"text-sm\" style=\"color: var(--text-secondary)\">Files missing from disk for two consecutive scans. Reading history is kept unless purged; items return automatically if their files come back.</p></div><div class=\"flex flex-wrap items-center gap-2\"><a href=\"/admin/archived\" class=\"btn btn-secondary\">View Archived</a> <button type=\"button\" @click=\"purgeArchivedItems()\" class=\"btn btn-secondary\">")
 			if templ_7745c5c3_Err != nil {
 				return templ_7745c5c3_Err
 			}