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/Header.tsx

@@ -1,6 +1,6 @@
 import { forwardRef, type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
-import { Youtube } from "lucide-react";
+import { YouTubeIcon } from "../lib/brandIcons";
 import type { Me } from "../lib/api";
 import SearchBar from "./SearchBar";
 import PlexSearchBox from "./PlexSearchBox";
@@ -61,7 +61,7 @@ const Header = forwardRef<
         onGo={() => onYtSearch(trimmed)}
         goLabel={t("header.searchYoutube")}
         goTitle={t("header.searchYoutubeTip")}
-        goIcon={<Youtube className="w-4 h-4" />}
+        goIcon={<YouTubeIcon className="w-4 h-4" />}
         goDisabled={!trimmed || me.is_demo}
       />
     );