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/Welcome.tsx

@@ -478,7 +478,7 @@ function AuthCard({ verify }: { verify: VerifyEntry }) {
     setMode("forgot");
   };
 
-  async function onSubmit(e: React.FormEvent) {
+  async function onSubmit(e: React.SubmitEvent<HTMLFormElement>) {
     e.preventDefault();
     setAttempt((n) => n + 1);
     reset();
@@ -495,6 +495,7 @@ function AuthCard({ verify }: { verify: VerifyEntry }) {
       return;
     }
     setBusy(true);
+    // eslint-disable-next-line react-hooks/todo -- the React Compiler cannot lower try/finally yet, so the enclosing component or hook stays uncompiled; pinned in compilerCoverage, burned down in E32 S3
     try {
       if (mode === "signin") {
         await api.passwordLogin(mail, password);
@@ -538,7 +539,7 @@ function AuthCard({ verify }: { verify: VerifyEntry }) {
     }
   }
 
-  async function onDemo(e: React.FormEvent) {
+  async function onDemo(e: React.SubmitEvent<HTMLFormElement>) {
     e.preventDefault();
     setDemoError("");
     const mail = demoEmail.trim().toLowerCase();
@@ -547,6 +548,7 @@ function AuthCard({ verify }: { verify: VerifyEntry }) {
       return;
     }
     setDemoBusy(true);
+    // eslint-disable-next-line react-hooks/todo -- the React Compiler cannot lower try/finally yet, so the enclosing component or hook stays uncompiled; pinned in compilerCoverage, burned down in E32 S3
     try {
       const r = await api.demoLogin(mail);
       if (r.authenticated) window.location.reload();