feat: on-demand topic tests with shared question bank

Adds a /topic-test route where learners can take a 5-question test on any
eligible topic at any time. Questions come from a shared, admin-curated
question_bank — no LLM calls on the user path. Points feed the existing
leaderboard with a 10pt/topic/week cap (per ISO week) so the bank can't be
farmed, and repeats from a thin bank yield 0 points.

- New PB collections: question_bank, on_demand_attempts (+ migrations and
  setup-pb-collections.mjs entries).
- db.js: un-deprecates getQuizBank/setQuizBank against question_bank so the
  existing admin TestManager panel becomes functional again; adds
  saveOnDemandAttempt, getOnDemandPointsThisWeek, getUserSeenQuestionIds,
  getAllOnDemandAttempts, isoWeekKey.
- testService.js: getEligibleTopicsForOnDemand, startOnDemandTest (unseen-
  first draw), finishOnDemandTest (cap enforcement + leaderboard upsert).
- New TopicTest page, route, and nav entry; weekly test flow untouched.
- Leaderboard folds on-demand 100%s into perfect-score count and merges
  on-demand attempts into the recent activity feed.
- Spec: docs/on-demand-tests-spec.md with ADRs and extension points.
- Tests: 5 new vitest cases covering eligibility, draw fallback, scoring,
  partial cap, and exhausted cap (85/85 total).

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

src/App.jsx

@@ -1,5 +1,5 @@
 import { Routes, Route, Navigate, Link } from 'react-router-dom'
-import { BookOpen, CheckSquare, LayoutDashboard, Trophy, Settings, LogOut } from 'lucide-react'
+import { BookOpen, CheckSquare, LayoutDashboard, Trophy, Settings, LogOut, Target } from 'lucide-react'
 import { useApp } from './store/AppContext'
 import Mark from './components/ui/Mark'
 import BuildStamp from './components/ui/BuildStamp'
@@ -12,6 +12,7 @@ import Dashboard from './pages/Dashboard'
 import Admin from './pages/Admin'
 import Leren from './pages/Leren'
 import Testen from './pages/Testen'
+import TopicTest from './pages/TopicTest'
 import Leaderboard from './pages/Leaderboard'
 
 // Protected Route Wrapper
@@ -50,6 +51,7 @@ const ProtectedRoute = ({ children, requireAdmin, skipEnrollmentGate }) => {
           <Link to="/" className="hover:text-accent-soft transition-colors flex items-center gap-2"><LayoutDashboard size={16}/> Dashboard</Link>
           <Link to="/learn" className="hover:text-accent-soft transition-colors flex items-center gap-2"><BookOpen size={16}/> Learn</Link>
           <Link to="/test" className="hover:text-accent-soft transition-colors flex items-center gap-2"><CheckSquare size={16}/> Test</Link>
+          <Link to="/topic-test" className="hover:text-accent-soft transition-colors flex items-center gap-2"><Target size={16}/> Topic Test</Link>
           <Link to="/leaderboard" className="hover:text-accent-soft transition-colors flex items-center gap-2"><Trophy size={16}/> Leaderboard</Link>
           {state.currentUser.role === 'admin' && (
             <Link to="/admin" className="hover:text-accent-soft transition-colors flex items-center gap-2">
@@ -77,6 +79,7 @@ const ProtectedRoute = ({ children, requireAdmin, skipEnrollmentGate }) => {
           <Link to="/" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><LayoutDashboard size={20}/><span className="text-[10px] mt-1 font-medium">Home</span></Link>
           <Link to="/learn" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><BookOpen size={20}/><span className="text-[10px] mt-1 font-medium">Learn</span></Link>
           <Link to="/test" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><CheckSquare size={20}/><span className="text-[10px] mt-1 font-medium">Test</span></Link>
+          <Link to="/topic-test" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><Target size={20}/><span className="text-[10px] mt-1 font-medium">Topic</span></Link>
           <Link to="/leaderboard" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><Trophy size={20}/><span className="text-[10px] mt-1 font-medium">Score</span></Link>
           {state.currentUser.role === 'admin' && (
             <Link to="/admin" className="flex flex-col items-center p-2 text-fg-muted hover:text-teal"><Settings size={20}/><span className="text-[10px] mt-1 font-medium">Admin</span></Link>
@@ -105,6 +108,7 @@ function App() {
         <Route path="/" element={<ProtectedRoute><Dashboard /></ProtectedRoute>} />
         <Route path="/learn" element={<ProtectedRoute><Leren /></ProtectedRoute>} />
         <Route path="/test" element={<ProtectedRoute><Testen /></ProtectedRoute>} />
+        <Route path="/topic-test" element={<ProtectedRoute><TopicTest /></ProtectedRoute>} />
         <Route path="/leaderboard" element={<ProtectedRoute><Leaderboard /></ProtectedRoute>} />
         <Route path="/admin/*" element={<ProtectedRoute requireAdmin={true}><Admin /></ProtectedRoute>} />
       </Routes>