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/board.py

@@ -791,23 +791,29 @@ async def create_page(request: Request, title: str = Query(default=""),
     """Create a new Markdown page, optionally as a sub-page."""
     user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
     ws_key = project if project else (user.get("login", "Bruno") if user else "Bruno")
-    with get_conn() as conn:
-        # Compute next sort_order for this parent
-        next_order = 0
-        parent_val = parent_id if parent_id > 0 else None
-        row = conn.execute(
-            "SELECT COALESCE(MAX(sort_order), -1) + 1 FROM pages WHERE workspace=? AND parent_id IS ?",
-            (ws_key, parent_val),
-        ).fetchone()
-        if row:
-            next_order = row[0]
-        cur = conn.execute(
-            "INSERT INTO pages (workspace, title, parent_section, parent_id, sort_order) VALUES (?,?,?,?,?)",
-            (ws_key, title, section, parent_val, next_order),
-        )
-        conn.commit()
-        page_id = cur.lastrowid
-    return {"status": "ok", "id": page_id, "title": title, "workspace": ws_key, "parent_id": parent_id}
+    page_title = title.strip() if title else "Untitled"
+    try:
+        with get_conn() as conn:
+            # Compute next sort_order for this parent
+            next_order = 0
+            parent_val = parent_id if parent_id > 0 else None
+            row = conn.execute(
+                "SELECT COALESCE(MAX(sort_order), -1) + 1 FROM pages WHERE workspace=? AND parent_id IS ?",
+                (ws_key, parent_val),
+            ).fetchone()
+            if row:
+                next_order = row[0]
+            cur = conn.execute(
+                "INSERT INTO pages (workspace, title, parent_section, parent_id, sort_order) VALUES (?,?,?,?,?)",
+                (ws_key, page_title, section, parent_val, next_order),
+            )
+            conn.commit()
+            page_id = cur.lastrowid
+        return {"status": "ok", "id": page_id, "title": page_title, "workspace": ws_key, "parent_id": parent_id}
+    except Exception as e:
+        logger.error("create_page failed: %s", e)
+        from fastapi.responses import JSONResponse
+        return JSONResponse({"error": "Failed to create page", "detail": str(e)}, status_code=500)
 
 
 @router.get("/api/pages/{page_id}")