build(frontend): close the lint gaps the E32 audit measured

eslint now also enforces:
- the React Compiler diagnostics that `recommended` leaves out (todo,
  memo-dependencies and ten zero-hit tripwires);
- a description on every suppression, and no blanket disables;
- no focused or skipped tests (vitest and playwright);
- the typed pair no-floating-promises and no-deprecated.

Lint also covers e2e/ and the TypeScript build configs, which `eslint .`
had been skipping in silence.

Every hit is fixed or suppressed inline with a named reason:
- The 31 try statements the compiler cannot lower yet carry a suppression
  until S3 rewrites them. Five other compiler skips were plain fixes:
  a module counter bumped inside a hook, a ref read in a default
  parameter, and a local named like the <section> it renders.
- The real defects behind floating promises are fixed. ChatDock threw at
  nobody when the device key store could not be opened. VideoEditor's
  play() rejection went unhandled. loadYouTubeApi never rejected, so a
  blocked IFrame API left the player on an empty stage forever; it now
  fails on a script error or after 15 s, shows its own error with the
  way out, and lets the next open try again.
- MutableRefObject, FormEvent and lucide's deprecated brand icon are
  replaced. The YouTube glyph now lives in lib/brandIcons.
- The lint-probe harness lets its virtual file names into TypeScript's
  default project, so the contract tests still run the real config.

frontend/src/components/PlexPlayer.tsx

@@ -27,7 +27,7 @@ import {
   Volume2,
   VolumeX,
 } from "lucide-react";
-import { api, HttpError, type PlexTrackNaming } from "../lib/api";
+import { api, HttpError, type PlexPlaySession, type PlexTrackNaming } from "../lib/api";
 import { notifyActionError } from "../lib/actionErrors";
 import {
   audioOrdForLang,
@@ -418,7 +418,9 @@ export default function PlexPlayer({ itemId, onClose, queue, fromStart = false }
       // "Preparing stream…" for a not-yet-known session while the plexSession request is in flight —
       // it's re-set honestly from the response below.
       setSessionIsTranscode(false);
-      let sess;
+      // Initialised, not a bare `let sess;`: the compiler's analysis read an unassigned local as a
+      // value from OUTSIDE this callback and asked for `sess.hw` as a dependency (memo-dependencies).
+      let sess: PlexPlaySession | null = null;
       try {
         // Multi-audio → request the multi-rendition session (no single `audio` ordinal); the track is
         // selected client-side after the manifest loads.
@@ -724,7 +726,7 @@ export default function PlexPlayer({ itemId, onClose, queue, fromStart = false }
       // sessGenRef is a LIVE counter: bumping it is how the unmount tells every in-flight session
       // that its response no longer belongs to anything, and a value captured when the effect ran
       // would invalidate a generation that has since been superseded instead of the current one.
-      // eslint-disable-next-line react-hooks/exhaustive-deps
+      // eslint-disable-next-line react-hooks/exhaustive-deps -- sessGenRef is a LIVE counter: unmount must bump the current generation, not a copy
       sessGenRef.current++;
       if (hlsRef.current) {
         hlsRef.current.destroy();
@@ -837,7 +839,7 @@ export default function PlexPlayer({ itemId, onClose, queue, fromStart = false }
         video.currentTime = rel; // native seek within the loaded region keeps playing on its own
         if (play) video.play().catch(() => {});
       } else {
-        loadSession(T, wasPlaying); // session restart: only auto-resume if we were playing
+        void loadSession(T, wasPlaying); // session restart: only auto-resume if we were playing
       }
     },
     [loadSession],