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/BootGate.dom.test.tsx

@@ -23,13 +23,14 @@ import i18n from "../i18n";
 
 const renders: { page: string; lang: string }[] = [];
 let mounts = 0;
+const countMount = () => {
+  mounts++; // outside the component: the compiler cannot lower `++` on a module variable in one
+};
 function Probe() {
   const { page } = useNavigation();
   const { i18n: inst } = useTranslation();
   renders.push({ page, lang: inst.language });
-  useEffect(() => {
-    mounts++;
-  }, []);
+  useEffect(countMount, []);
   return <div data-testid="app">{page}</div>;
 }
 
@@ -226,7 +227,9 @@ describe("BootGate", () => {
     const qc = mount();
     await screen.findByTestId("app");
     // Anything that re-renders the gate must leave it alone: a pref save, a background refetch.
-    act(() => qc.setQueryData(qk.me(), account({ preferences: { startup: "last" } })));
+    act(() => {
+      qc.setQueryData(qk.me(), account({ preferences: { startup: "last" } }));
+    });
     await act(() => new Promise((r) => setTimeout(r, 20)));
 
     expect(reload).not.toHaveBeenCalled();
@@ -241,7 +244,9 @@ describe("BootGate", () => {
     vi.stubGlobal("location", { ...window.location, reload });
 
     // What every pref save does to the cache (usePref's mergePrefsCache): a new `me` for the same account.
-    act(() => qc.setQueryData(qk.me(), account({ preferences: { language: "hu" } })));
+    act(() => {
+      qc.setQueryData(qk.me(), account({ preferences: { language: "hu" } }));
+    });
     await act(() => new Promise((r) => setTimeout(r, 20)));
 
     expect(reload).not.toHaveBeenCalled();