refactor(frontend): the two players — one real ordering bug avoided, five suppressions gone (E27 S2)

The interesting part of this batch is a change that was WRONG and the test suite said so.

PlayerModal synced its local watch-status mirror and `currentVideoId` from an effect on
`active.id`. Moving that into render is right — as an effect there was a frame per queue advance
showing the new episode's chrome over the previous item's watch state, with `navigated` still
true so the "you have navigated away" affordance flashed. But the same effect also advanced
`currentIdRef`, and that line must NOT move: useYtProgress's per-item cleanup persists the
OUTGOING item's position and guards it on `currentIdRef.current === id`. React runs every
cleanup before any setup, so in an effect the ref still names the item being left. Advanced to
render time the flip happens first, the checkpoint is skipped, and stepping next→prev back to an
item resumes from the frozen launch queue's stale position. "resumes an item played earlier in
the SAME session" caught it immediately (748 instead of 830); the ref write stays in its own
effect with the ordering written down.

The rest:
- PlayerModal's keyboard handler is a useEffectEvent, so the "bound once, reads live state"
  contract is enforced instead of asserted. `focusModal` is a useCallback now — it reads a ref
  and nothing else, and three hooks take it as a parameter where a fresh identity would spread.
- PlexPlayer's session reclaim called `loadSession` from inside loadSession's own useCallback,
  which the checker reads as a forward reference. Routed through a ref, the file's existing
  answer for exactly this (detachSessionRef, cancelAutoSkipRef).
- PlexPlayer's item-load effect excluded `prefs` by hand so a track pick from the player's own
  menu would not double-load the session. The two language prefs go through a ref instead —
  "latest value, not a trigger", said in code rather than in a comment.
- PlexPlayer closes its up-next card during the render that changes `id`, not a commit later.
- The one PlexPlayer directive that stays is the live session counter, whose cleanup must bump
  the CURRENT value: the rule's advice to copy it into a variable is precisely wrong there, and
  the comment now says why rather than pointing at another comment.

Suppressions 75 -> 70; exhaustive-deps 20 -> 17.

frontend/eslint-suppressions.json

@@ -85,11 +85,6 @@
       "count": 1
     }
   },
-  "src/components/PlayerModal.tsx": {
-    "react-hooks/set-state-in-effect": {
-      "count": 1
-    }
-  },
   "src/components/Playlists.tsx": {
     "react-hooks/immutability": {
       "count": 2
@@ -106,9 +101,6 @@
   "src/components/PlexPlayer.tsx": {
     "react-hooks/immutability": {
       "count": 1
-    },
-    "react-hooks/set-state-in-effect": {
-      "count": 1
     }
   },
   "src/components/PlexSearchBox.tsx": {