feat: v4.0.2 — qualité & robustesse (session expiry UX, validation, mobile, tests)

- Session expiry: redirects ajoutent ?expired=1 → bannière "Session expired" sur login
- Page titles: titre vide → 'Untitled' par défaut (au lieu de chaîne vide)
- Error handling: try/catch dans create_page avec message user-friendly (500)
- Mobile responsive: sidebar slide-in, modales centrées, landing page adaptative
- 10 nouveaux tests de non-régression: landing, register, 404, validation, duplicate
- 143 tests passent (133 + 10)

app/routers/auth.py

@@ -55,6 +55,7 @@ body{background:#191919;color:#fff;font-family:-apple-system,BlinkMacSystemFont,
     <button class="tab active" onclick="switchTab('login')" id="tab-login">Login</button>
     <button class="tab" onclick="switchTab('register')" id="tab-register">Register</button>
   </div>
+  <div id="expired-msg" class="success" style="display:none">⚠️ Your session has expired. Please log in again.</div>
   <div id="error-msg" class="error"></div>
   <div id="success-msg" class="success"></div>
   <form id="login-form" onsubmit="handleLogin(event)">
@@ -76,6 +77,8 @@ body{background:#191919;color:#fff;font-family:-apple-system,BlinkMacSystemFont,
   </div>
 </div>
 <script>
+// Show session expired banner if ?expired=1 in URL
+(function(){if(location.search.includes('expired=1')){var el=document.getElementById('expired-msg');if(el)el.style.display='block';}})();
 let mode='login';
 function switchTab(t){mode=t;document.querySelectorAll('.tab').forEach(el=>el.classList.remove('active'));document.getElementById('tab-'+t).classList.add('active');document.getElementById('name-group').style.display=t==='register'?'block':'none';document.getElementById('submit-btn').textContent=t==='register'?'Register':'Login';document.getElementById('error-msg').style.display='none';document.getElementById('success-msg').style.display='none';var lbl=t==='register'?'Register':'Login';var e1=document.getElementById('gitea-btn-label');var e2=document.getElementById('github-btn-label');if(e1)e1.textContent=lbl;if(e2)e2.textContent=lbl;}
 function togglePassword(){var pw=document.getElementById('password');var btn=pw.parentElement.querySelector('.pw-toggle');if(pw.type==='password'){pw.type='text';btn.textContent='🙈';}else{pw.type='password';btn.textContent='👁';}}