Fix L19/L73: replace setTimeout focus hack with double-rAF; unify probe verb

L19: App.tsx replaced `setTimeout(() => focus(), 60)` in the "New download"
     palette action with `requestAnimationFrame(() => requestAnimationFrame(...))`
     to wait exactly one React render + paint cycle rather than an arbitrary 60ms
     timer that could race on slow machines.

L73: DownloadBar's probe button label changed from "Fetch" to "Check URL" (hint
     and aria-label both updated). Placeholder text updated to match. This
     distinguishes it from LibraryView's "Index" action, which catalogs an entire
     channel/playlist, making both labels clearly meaningful in context.

typecheck + 242 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CODE-AUDIT.md

@@ -414,7 +414,7 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
   feedback and silently never matches (main's `matchesUrl` swallows the error).
 - [x] **L18 — Terminal nav item shown when custom commands are off** — leads to a gated dead-end
   view; consider hiding/disabling it.
-- [ ] **L19 — `App.tsx` focus hack** — `setTimeout(() => …focus(), 60)` after a tab switch.
+- [x] **L19 — `App.tsx` focus hack** — `setTimeout(() => …focus(), 60)` after a tab switch.
 - [x] **L20 — `youtubePlayerClient` is free text** with no allowlist/validation; a typo passes
   straight to yt-dlp's `--extractor-args`.
 - [ ] **L21 — Inconsistent in-component error handling.** SettingsView funnels the app-update
@@ -514,7 +514,7 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
   known path.
 - [x] **L72 — History re-download drops the thumbnail** (passes only title/channel), so the
   re-queued row loses its thumbnail until re-probed.
-- [ ] **L73 — Two verbs for the same probe action** — DownloadBar "Fetch" vs LibraryView "Index".
+- [x] **L73 — Two verbs for the same probe action** — DownloadBar "Fetch" vs LibraryView "Index".
 - [x] **L74 — Accent swatches are triple-labeled** (`aria-pressed` + `aria-label` + `title`).
 - [x] **L75 — Update-token field always visible** in the Software-update card, even when no update
   is pending — buries an advanced/rarely-needed input.