feat: theme-grouped pickers, theme-session content panel, theme/topic naming

- Admin Topic Quizzes (was Quizzes): topics are now grouped under
  collapsible theme headers with per-theme counts. Topics without a
  theme fall into a "No theme" bucket rendered last.
- /topic-test picker: eligible topics grouped by theme so learners can
  scan a curriculum theme and drill its topics on demand.
- Fix admin Theme Content panel (was Learning Content): it was empty
  because content moved to the theme_sessions collection in an earlier
  refactor while the panel still queried the legacy per-topic content
  table. Rewrites ContentManager to read db.getAllThemeSessions and
  render the emit_theme_session schema (title, intro, topic sections,
  connections, key takeaways). Adds db.getAllThemeSessions and
  db.deleteThemeSession.
- Disambiguate theme vs topic across the app: the weekly curriculum
  test is now "Theme Test" (nav, page heading, Dashboard card, button,
  explainer); the on-demand bank test stays "Topic Test". Admin nav
  also clarified to "Theme Content" / "Topic Quizzes".

No schema changes. 85/85 tests still pass, build green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/Admin/index.jsx

@@ -87,8 +87,8 @@ const Admin = () => {
 
   const navItems = [
     { key: 'sources', icon: Database, label: 'Sources' },
-    { key: 'content', icon: Layers, label: 'Content' },
-    { key: 'tests', icon: CheckSquare, label: 'Quizzes' },
+    { key: 'content', icon: Layers, label: 'Theme Content' },
+    { key: 'tests', icon: CheckSquare, label: 'Topic Quizzes' },
     { key: 'curriculum', icon: CalendarDays, label: 'Curriculum' },
     { key: 'graph', icon: Network, label: 'Graph' },
     { key: 'team', icon: Users, label: 'Team' },
@@ -162,16 +162,16 @@ const Admin = () => {
 
         {activeTab === 'content' && (
           <div className="animate-in fade-in duration-300 max-w-4xl mx-auto">
-            <h1 className="text-3xl text-teal mb-2">Learning Content</h1>
-            <p className="text-fg-muted mb-8">Manage, refine, or regenerate AI-generated learning modules for each knowledge topic.</p>
+            <h1 className="text-3xl text-teal mb-2">Theme Content</h1>
+            <p className="text-fg-muted mb-8">Weekly theme sessions generated by the AI for the active curriculum. Each session covers all topics in that week's theme.</p>
             <ContentManager />
           </div>
         )}
 
         {activeTab === 'tests' && (
           <div className="animate-in fade-in duration-300 max-w-4xl mx-auto">
-            <h1 className="text-3xl text-teal mb-2">Question Banks</h1>
-            <p className="text-fg-muted mb-8">Pre-generate and review quiz questions for each topic to eliminate loading times for users.</p>
+            <h1 className="text-3xl text-teal mb-2">Topic Question Banks</h1>
+            <p className="text-fg-muted mb-8">Pre-generate and review per-topic quiz questions, grouped by theme. These power both the weekly theme test and the on-demand Topic Test.</p>
             <TestManager />
           </div>
         )}