annotations v2: redesign

Reskin to v2 surface/accent tokens + JetBrains Mono headings to match
_docs/ui_design/v2/plugin/annotations.html. Add scrubber with class-colored
annotation marks, canvas top bar (zoom/cursor/dims), floating AI-detection
banner, multi-band gradient rows in the annotations sidebar, class-distribution
summary footer, and DOM-overlay bbox labels with affiliation icon + readiness
dot. Split VideoPlayer chrome out into the page-level controls row
(transport/frame-step/save/delete/AI-detect/mute/volume) and a new Scrubber
component; player events replace 200ms polling.

Other:
- Auth dev bypass via VITE_DEV_AUTH_BYPASS (gated on import.meta.env.DEV).
- Mount SavedAnnotationsProvider in App so AnnotationsPage doesn't crash.
- Extract hexToRgba to src/class-colors and time helpers to
  src/features/annotations/time.ts (dedup across CanvasEditor / Sidebar /
  AnnotationsPage).
- CanvasEditor: shallow-compare label chips before commit, NaN-guard
  annotation-time parser, cancel cursor RAF on unmount.
- AnnotationsPage: track AI-banner close timer, push initial volume to the
  <video> on media change, drop the duplicate parent muted state.
- Fixed sidebar widths (resize handles removed per design).

src/App.tsx

@@ -1,6 +1,6 @@
 import { Routes, Route, Navigate } from 'react-router-dom'
 import { AuthProvider, ProtectedRoute } from './auth'
-import { Header, FlightProvider } from './components'
+import { Header, FlightProvider, SavedAnnotationsProvider } from './components'
 import { LoginPage } from './features/login'
 import { FlightsPage } from './features/flights'
 import { AnnotationsPage } from './features/annotations'
@@ -18,19 +18,21 @@ export default function App() {
           element={
             <ProtectedRoute>
               <FlightProvider>
-                <div className="flex flex-col h-screen">
-                  <Header />
-                  <div className="flex-1 overflow-hidden">
-                    <Routes>
-                      <Route path="/flights" element={<FlightsPage />} />
-                      <Route path="/annotations" element={<AnnotationsPage />} />
-                      <Route path="/dataset" element={<DatasetPage />} />
-                      <Route path="/admin" element={<AdminPage />} />
-                      <Route path="/settings" element={<SettingsPage />} />
-                      <Route path="*" element={<Navigate to="/flights" replace />} />
-                    </Routes>
+                <SavedAnnotationsProvider>
+                  <div className="flex flex-col h-screen">
+                    <Header />
+                    <div className="flex-1 overflow-hidden">
+                      <Routes>
+                        <Route path="/flights" element={<FlightsPage />} />
+                        <Route path="/annotations" element={<AnnotationsPage />} />
+                        <Route path="/dataset" element={<DatasetPage />} />
+                        <Route path="/admin" element={<AdminPage />} />
+                        <Route path="/settings" element={<SettingsPage />} />
+                        <Route path="*" element={<Navigate to="/flights" replace />} />
+                      </Routes>
+                    </div>
                   </div>
-                </div>
+                </SavedAnnotationsProvider>
               </FlightProvider>
             </ProtectedRoute>
           }