feat: administration — users, roles, stats, audit

DB:
- login_history table (user_id, ip, user_agent, timestamp)
- Migration v2.5: alter users + create login_history

Auth:
- Premier utilisateur = admin (is_admin=1)
- _log_login() après chaque connexion (register, local-login, OAuth)

Backend (app/routers/admin.py):
- admin_required middleware (vérifie is_admin)
- GET  /api/admin/users     → liste users + stats par user
- POST /api/admin/users     → créer user
- PUT  /api/admin/users/:id → modifier (name, email, password, admin, active)
- DELETE /api/admin/users/:id → supprimer + cascade
- GET  /api/admin/stats     → totaux globaux
- GET  /api/admin/audit     → historique login

Frontend (settings.html):
- Nav Admin visible seulement si userIsAdmin
- Users & Roles: stats cards, create/edit/delete users, table complète
- Audit Log: historique login avec date, IP, user-agent
- CSS professionnel: table-wrap, admin-table, stat-card, role-badge, status-dot

app/db.py

@@ -37,6 +37,14 @@ def init_db():
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
             );
 
+            CREATE TABLE IF NOT EXISTS login_history (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                user_id INTEGER NOT NULL REFERENCES users(id),
+                ip_address TEXT DEFAULT '',
+                user_agent TEXT DEFAULT '',
+                logged_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            );
+
             CREATE TABLE IF NOT EXISTS user_tokens (
                 id INTEGER PRIMARY KEY AUTOINCREMENT,
                 gitea_user_id INTEGER NOT NULL UNIQUE,
@@ -356,6 +364,21 @@ def init_db():
                 conn.execute(f"ALTER TABLE users ADD COLUMN {col} {'TEXT' if col in ('password_hash','last_login','locked_until') else 'INTEGER NOT NULL DEFAULT ' + ('1' if col=='is_active' else '0')}")
             except sqlite3.OperationalError:
                 pass
+        # v2.5: Login history
+        try:
+            conn.execute("ALTER TABLE users ADD COLUMN is_admin INTEGER NOT NULL DEFAULT 0")
+        except sqlite3.OperationalError:
+            pass
+        try:
+            conn.execute("""CREATE TABLE IF NOT EXISTS login_history (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                user_id INTEGER NOT NULL REFERENCES users(id),
+                ip_address TEXT DEFAULT '',
+                user_agent TEXT DEFAULT '',
+                logged_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )""")
+        except sqlite3.OperationalError:
+            pass
         conn.commit()