Phase 5: library & stats

- Full library home page: question list with per-user mastery stats,
  search/source filter, sort (A-Z, weakest first, most-seen), source
  breakdown in header, Take a test CTA.
- GET/POST /questions/{id}: view and edit question text, source, answers;
  radio-select correct answer; shows seen×/correct% stat.
- POST /questions/{id}/delete: hard delete (cascades to answers via FK).
- repo: ListQuestions supports SortWeakest/SortMostSeen via LEFT JOIN;
  added CountBySource, UpdateQuestion, UpdateAnswers, DeleteQuestion.
- render: added pct template func (correct*100/seen).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/templates/home.html

@@ -1,7 +1,79 @@
 {{define "content"}}
-<h1 class="text-2xl font-bold text-gray-800 mb-2">Library</h1>
-<p class="text-gray-500 text-sm">
-  No questions yet.
-  <a href="/upload" class="text-blue-600 hover:underline">Upload a document</a> to get started.
-</p>
+<div class="mb-5 flex items-baseline justify-between">
+  <h1 class="text-2xl font-bold text-gray-800">Library</h1>
+  <a href="/upload" class="text-sm text-blue-600 hover:underline">+ Upload</a>
+</div>
+
+{{if eq .TotalQ 0}}
+<div class="text-center py-16 text-gray-400">
+  <p class="text-lg">No questions yet.</p>
+  <a href="/upload" class="mt-4 inline-block text-blue-600 hover:underline text-sm">Upload a document to get started</a>
+</div>
+{{else}}
+
+<div class="mb-5 text-sm text-gray-500">
+  {{.TotalQ}} question{{if ne .TotalQ 1}}s{{end}} · {{.TotalA}} answer{{if ne .TotalA 1}}s{{end}}
+  {{if .SourceStats}}
+  <span class="mx-1">·</span>
+  {{range $i, $s := .SourceStats}}{{if $i}}<span class="mx-0.5 text-gray-300">|</span>{{end}}<span>{{$s.Source}} ({{$s.Count}})</span>{{end}}
+  {{end}}
+</div>
+
+<form method="get" action="/" class="flex flex-wrap gap-2 mb-4">
+  <input type="text" name="q" value="{{.Search}}" placeholder="Search…"
+         class="flex-1 min-w-0 border border-gray-300 rounded-md px-3 py-1.5 text-sm
+                focus:outline-none focus:ring-2 focus:ring-blue-500">
+  {{if .SourceStats}}
+  <select name="source" onchange="this.form.submit()"
+          class="border border-gray-300 rounded-md px-2 py-1.5 text-sm
+                 focus:outline-none focus:ring-2 focus:ring-blue-500 bg-white">
+    <option value="">All sources</option>
+    {{range .SourceStats}}
+    <option value="{{.Source}}" {{if eq .Source $.SelectedSource}}selected{{end}}>{{.Source}}</option>
+    {{end}}
+  </select>
+  {{end}}
+  <select name="sort" onchange="this.form.submit()"
+          class="border border-gray-300 rounded-md px-2 py-1.5 text-sm
+                 focus:outline-none focus:ring-2 focus:ring-blue-500 bg-white">
+    <option value="alpha" {{if eq .Sort "alpha"}}selected{{end}}>A–Z</option>
+    <option value="weakest" {{if eq .Sort "weakest"}}selected{{end}}>Weakest first</option>
+    <option value="seen" {{if eq .Sort "seen"}}selected{{end}}>Most seen</option>
+  </select>
+  <button type="submit"
+          class="bg-blue-600 hover:bg-blue-700 text-white px-4 py-1.5 rounded-md text-sm font-medium">
+    Search
+  </button>
+</form>
+
+{{if .Questions}}
+<div class="space-y-2">
+  {{range .Questions}}
+  <a href="/questions/{{.Q.ID}}"
+     class="block bg-white border border-gray-200 rounded-lg px-4 py-3 hover:border-blue-300 hover:shadow-sm transition-all">
+    <div class="flex items-start justify-between gap-4">
+      <p class="text-sm text-gray-800 line-clamp-2">{{.Q.Text}}</p>
+      <span class="text-xs text-gray-400 whitespace-nowrap mt-0.5 flex-shrink-0">
+        {{if .Stat}}{{.Stat.TimesSeen}}× · {{pct .Stat.TimesCorrect .Stat.TimesSeen}}%{{else}}—{{end}}
+      </span>
+    </div>
+    {{if .Q.Source}}
+    <p class="text-xs text-gray-400 mt-1">{{.Q.Source}}</p>
+    {{end}}
+  </a>
+  {{end}}
+</div>
+{{else}}
+<p class="text-center py-8 text-gray-400 text-sm">No questions match your filter.</p>
+{{end}}
+
+<div class="mt-6 text-center">
+  <a href="/test/new"
+     class="inline-block bg-blue-600 hover:bg-blue-700 text-white px-8 py-2.5 rounded-md
+            text-sm font-semibold shadow-sm">
+    Take a test
+  </a>
+</div>
+
+{{end}}
 {{end}}