feat(whats-new): remote release notes with dev workspace mode (#1058)

* feat(whats-new): remote release notes with dev workspace mode

Add WHATS_NEW.md, CI whats-new.md asset upload, and client fetch/cache
with embedded fallbacks. Dev and -dev builds read the full file from the
repo for debugging; RC/stable download the release asset on first use.

* fix(whats-new): render ## headings and add changelog tab

Parse h2 sections in release-notes markdown; load changelog alongside
highlights and let users switch views on the What's New page.

* fix(whats-new): prefetch on startup and fix CI typecheck prebuild

Prefetch whats-new asset when the shell loads on RC/stable builds.
Run prebuild:release-notes before tsc and coverage jobs so the
gitignored generated bundle exists in CI.

* docs: CHANGELOG and credits for What's New remote notes (PR #1058)

* fix(whats-new): always slice embedded release notes to current line

Drop full CHANGELOG embed for -dev bundles; tauri:dev still reads live
markdown from the repo. Ignore all of src/generated/ in git.

* fix(whats-new): fetch release asset via Rust to bypass CORS

Route whats-new.md download through fetch_url_bytes; rename the
technical tab label; add fetch unit tests (PR #1058 review).

src/app/AppShell.tsx

@@ -44,6 +44,7 @@ import { useOfflineBrowseContext } from '../hooks/useOfflineBrowseContext';
 import { offlineBrowseNavFlags } from '../utils/offline/offlineBrowseContext';
 import { useWindowFullscreenState } from '../hooks/useWindowFullscreenState';
 import { useNowPlayingTrayTitle } from '../hooks/useNowPlayingTrayTitle';
+import { usePrefetchReleaseNotes } from '../hooks/usePrefetchReleaseNotes';
 import { useTrayMenuI18n } from '../hooks/useTrayMenuI18n';
 import { useServerCapabilitiesProbe } from '../hooks/useServerCapabilitiesProbe';
 import { useQueueResizer } from '../hooks/useQueueResizer';
@@ -164,6 +165,7 @@ export function AppShell() {
   // Post-update changelog is now surfaced via a dismissible banner in the
   // sidebar (WhatsNewBanner) that links to the /whats-new page — no auto
   // modal takeover on startup.
+  usePrefetchReleaseNotes();
 
   const [isSidebarCollapsed, setIsSidebarCollapsed] = useState(readInitialSidebarCollapsed);
   const isMainScrolling = useMainScrollingIndicator(location.pathname);