feat(a11y): touch-visible card controls + modal focus trap/restore (E4 S6)

UX-7 — hover-only card actions were `opacity-0 group-hover:opacity-100`: fine on
a mouse, but invisible AND still tappable on a touch device (no hover). New
`.reveal` primitive (index.css) gates the hide on `@media (hover: hover)`, so a
touch device keeps the control visible; its partner `.reveal-idle` is the idle
badge a control replaces (watched/in-progress pill under the watched-toggle),
faded on hover and dropped on touch so the two don't collide at the same corner.
Migrated the true controls — feed card action toolbar (VideoCard), Plex poster
card watched-toggle/info/add across all card variants + their swap badges
(plexCards), message pop-out (Messages), edit-interval pencil (Scheduler), and
saved-view star/rename/delete (SavedViewsWidget). Pure play-scrim overlays (the
whole card is the tap target) stay hover-only by design.

FE-9 — Modal.tsx had aria-modal but no focus management. Adds: a Tab/Shift+Tab
focus trap (topmost layer only, wraps at the edges and pulls escaped focus back);
initial focus into the dialog unless an autoFocus child already placed it; focus
restore to the trigger on close (captured in a useState initializer during render,
before commit runs autoFocus and moves activeElement inside); and aria-labelledby
wiring the dialog to its title.

Gate green (tsc, knip, lint 0-err, 247 vitest). Self-E2E (localdev): FE-9 trap
both directions + pull-back + Escape-restore-to-trigger + aria-labelledby verified;
UX-7 feed toolbar opacity 0 on desktop / 1 under mobile (hover:none) emulation,
Plex reveal buttons opacity 1 + reveal-idle badges display:none on touch.

frontend/src/components/VideoCard.tsx

@@ -62,7 +62,7 @@ function Actions({
     // rather than silently rendering a half-clipped control outside the card.
     <div
       className={clsx(
-        "flex flex-wrap opacity-0 group-hover:opacity-100 transition",
+        "flex flex-wrap reveal transition",
         dense ? "gap-0.5" : "gap-1",
       )}
     >