Add user bug reporting with admin triage (open/read/resolved)

Turns the /report-bug placeholder into a real form (POST /bug-reports,
optionally attributed to the logged-in user) and adds a "Segnalazioni bug"
section to /admin to view and triage them. A logged-in reporter can also
check their own report's status via GET /bug-reports/mine, since anonymous
submissions have no user to show a history to.

Status is a three-state lifecycle (open -> read -> resolved) rather than a
plain boolean, so an admin can acknowledge a report distinctly from actually
fixing it. The schema went through two migrations because the first one
(add bug_reports table) had already been applied against the running
instance with a `resolved` boolean before the three-state design was
decided, so a follow-up migration backfills it into `status` instead of
rewriting already-applied history.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/static/admin.html

@@ -30,6 +30,7 @@
     <span class="nav-tab" id="nav-round" onclick="switchView('round')">Round</span>
     <span class="nav-tab" id="nav-pending" onclick="switchView('pending')">Transazioni pendenti</span>
     <span class="nav-tab" id="nav-audit" onclick="switchView('audit')">Audit log</span>
+    <span class="nav-tab" id="nav-bugreports" onclick="switchView('bugreports')">Segnalazioni bug</span>
     <span class="spacer"></span>
     <span class="chain-status-pill">
       <span class="status-dot" id="chain-status-dot"></span>
@@ -153,6 +154,22 @@
       </div>
     </div>
 
+    <div class="view" id="view-bugreports">
+      <h2 class="section-title">Segnalazioni bug</h2>
+      <p class="hint">Segnalazioni inviate dagli utenti tramite la pagina "Segnala un bug".</p>
+
+      <div class="card">
+        <div class="table-wrap">
+          <table>
+            <thead>
+              <tr><th>ID</th><th>Descrizione</th><th>Contatto</th><th>Utente</th><th>Quando</th><th>Stato</th></tr>
+            </thead>
+            <tbody id="bugreports-tbody"></tbody>
+          </table>
+        </div>
+      </div>
+    </div>
+
   </main>
 </div>