feat: add People view with person cards and click-to-filter

Replace the tag-grouping people section with a dedicated PeopleView:
- Grid of face cluster cards showing representative photo thumbnail,
  person name, and photo count
- Click a card → navigates to all-photos filtered by that person's tag
- Inline rename via pencil icon on hover
- Empty state when no faces have been clustered yet

Wired into App.tsx as a section-level route alongside Map and Duplicates.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -2,6 +2,7 @@ import { useState } from 'react'
 import { Timeline } from './components/timeline/Timeline'
 import { DuplicatesView } from './components/duplicates/DuplicatesView'
 import { MapView } from './components/map/MapView'
+import { PeopleView } from './components/people/PeopleView'
 import { LeftSidebar } from './components/layout/LeftSidebar'
 import { RightSidebar } from './components/layout/RightSidebar'
 import { TopBar } from './components/layout/TopBar'
@@ -86,6 +87,8 @@ function App() {
               <MapView />
             ) : currentSection === 'duplicates' ? (
               <DuplicatesView />
+            ) : currentSection === 'people' ? (
+              <PeopleView />
             ) : (
               <Timeline />
             )}