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/ui/AnchoredPopover.tsx

@@ -231,7 +231,7 @@ interface PopoverSurfaceProps {
    *  take its name from. */
   ariaLabel?: string;
   focusManaged?: boolean;
-  initialFocus?: number | React.MutableRefObject<HTMLElement | null>;
+  initialFocus?: number | React.RefObject<HTMLElement | null>;
   /** The surface never receives pointer events — for a passive caption that must not swallow a click
    *  aimed at whatever it happens to cover during its close delay. Interactive hover cards (scrollable
    *  content, links) must NOT set this. */

frontend/src/components/ui/Toaster.tsx

@@ -205,7 +205,7 @@ export default function Toaster({
           {/* lib/toastDock is a one-slot registry: this identity changes only when a surface docks
               or undocks, and remounting is then the correct behaviour, not the hazard the rule
               warns about. */}
-          {/* eslint-disable-next-line react-hooks/static-components */}
+          {/* eslint-disable-next-line react-hooks/static-components -- a one-slot dock registry: the identity changes only on dock/undock, where a remount is right */}
           <Docked />
         </div>
       )}

frontend/src/components/ui/overlayOrder.ts

@@ -3,9 +3,11 @@ import { useState } from "react";
 // An overlay's toast-host rank (see the overlay-hosts note in Toaster). Its own module so Toaster exports
 // only components (Fast Refresh); the counter is module state, so there is exactly one sequence.
 let overlaySeq = 0;
+// Outside the hook: the React Compiler cannot lower `++` on a module variable inside one (react-hooks/todo).
+const nextOverlaySeq = () => ++overlaySeq;
 /** This overlay's rank among open overlays — taken once, when it mounts. Call it in the overlay
  *  itself, never in a component that can remount while the overlay stays open. */
 export function useOverlayOrder(): number {
-  const [order] = useState(() => ++overlaySeq);
+  const [order] = useState(nextOverlaySeq);
   return order;
 }

frontend/src/components/ui/sortableA11y.ts

@@ -65,7 +65,7 @@ export function useSortableA11y(describe: (id: UniqueIdentifier) => SortableSubj
           // dnd-kit reports the item over ITSELF in the pick-up tick (see above), and this flag is
           // the only thing separating that from a real move. A ref would be the wrong lifetime —
           // one drag, not the component.
-          // eslint-disable-next-line react-hooks/immutability
+          // eslint-disable-next-line react-hooks/immutability -- per-DRAG state the announcement closures share; a ref would live as long as the component
           moved = true;
           return t("common.dnd.movedOver", landing(active.id, over.id));
         },