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/lib/plexPlayerHooks.subtitle.dom.test.tsx

@@ -12,7 +12,7 @@
 import { describe, it, expect, vi, afterEach, beforeEach } from "vitest";
 import { act, cleanup, render, renderHook, waitFor } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
-import { createRef, type ReactNode, type MutableRefObject } from "react";
+import { createRef, type ReactNode, type RefObject } from "react";
 import { usePlexTracks } from "./plexPlayerHooks";
 import { api, type PlexItemDetail } from "./api";
 import { dismissError, getError } from "./errorDialog";
@@ -49,7 +49,7 @@ function mount(qc: QueryClient, { sessionK = 0, abs = 3600, loadStart = 0 } = {}
         videoRef: createRef<HTMLVideoElement>(),
         hlsRef: createRef<Hls>(),
         multiAudioRef: { current: false },
-        audioRef: { current: 0 } as MutableRefObject<number | null>,
+        audioRef: { current: 0 } as RefObject<number | null>,
         aoffRef: { current: 0 },
         absRef: { current: abs },
         loadStartRef: { current: loadStart },
@@ -325,7 +325,7 @@ function TrackHarness() {
     videoRef: createRef<HTMLVideoElement>(),
     hlsRef: createRef<Hls>(),
     multiAudioRef: { current: false },
-    audioRef: { current: 0 } as MutableRefObject<number | null>,
+    audioRef: { current: 0 } as RefObject<number | null>,
     aoffRef: { current: 0 },
     absRef: { current: 3600 },
     loadStartRef: { current: 0 },