refactor(ui): the popover engine and every render-phase ref write compile under the React Compiler

E32 S3. The compiler skipped 93 functions; it now skips 29 (try/finally shapes, two suppressions,
VirtualGrid). react-hooks/refs hits 245 -> 31.

- Popover engine: `ref={pop.refs.setReference}` made the compiler treat the whole popover handle as
  a ref, so every component holding one was skipped (21 call sites, the engine and its surface
  among them). The setter is destructured now; the same for useScrollFade and useReturnFocus.
- Render-phase `ref.current = x` writes moved to `useEffectEvent` where only effects read them,
  else to the new `useLatest` (written in a layout effect) / `useStableCallback`.
- FocusSafeButton (under every Button) read the focused element during render; it reads it through
  useSyncExternalStore, which React asks on every render instead of a cached memo.

Bugs this surfaced, fixed:
- Combobox: a chip could keep showing its raw id. The label cache was a ref an effect filled after
  the render that needed it; it is state merged during render now (test seen RED).
- useUndoable rendered from a ref plus a forced re-render; compiled, that memoizes a stale value.
  The history is state now, mirrored in a ref for the stable callbacks.
- ConfigPanel and the saved-views editor re-seeded their drafts in an effect, painting the stale
  draft for a frame; both adjust during render against the remembered key.
- Toaster's handover is written after commit instead of during render; a new test pins that the
  inherited set is taken once, at the takeover (seen RED on a per-render re-read).
- IssueComposer mutated a ref prop as a one-shot focus token; it is plain state.
- PlexBrowse wrote its info-scroll memory from an effect declared before the ref, past its own
  "one writer" rule; the writer comes first now and the effect goes through it.

The compiler ratchet drops to the measured 29 and now also requires FocusSafeButton and the popover
engine to compile.

frontend/src/components/BootGate.tsx

@@ -1,4 +1,4 @@
-import { useLayoutEffect, useRef, useState, type ReactNode } from "react";
+import { useEffectEvent, useLayoutEffect, useState, type ReactNode } from "react";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { useTranslation } from "react-i18next";
 import { api, getActiveAccount, setActiveAccount } from "../lib/api";
@@ -89,12 +89,11 @@ export default function BootGate({ children }: { children: ReactNode }) {
   //     orders its lists and writes its mail in the stored one, else English, and a Hungarian screen
   //     over English-ordered lists breaks "A→Z in the UI language's alphabet".
   const [readyFor, setReadyFor] = useState<number | null | undefined>(undefined);
-  // `me` is read for the identity it produced, so it rides a ref: a background refetch of the same
+  // `me` is read for the identity it produced, so it is an effect event: a background refetch of the same
   // account must not re-run the adoption over a language the user has just changed. That rule used
   // to live in a dep list that excluded `me`, which made the dep list load-bearing for correctness —
   // and the failure mode of getting it wrong was a page-reload loop, not a stale value.
-  const meRef = useRef(me);
-  meRef.current = me;
+  const adoptedMe = useEffectEvent(() => me);
   useLayoutEffect(() => {
     if (identity === undefined) return;
     if (readyFor !== undefined) {
@@ -107,7 +106,7 @@ export default function BootGate({ children }: { children: ReactNode }) {
       if (readyFor !== identity) location.reload();
       return;
     }
-    const account = meRef.current;
+    const account = adoptedMe();
     if (account && getActiveAccount() !== account.id) setActiveAccount(account.id);
     const lang = account?.preferences?.language;
     if (typeof lang === "string" && isSupported(lang)) {