fix: login → /workspaces, workspace tree filtered, sidebar CRUD

- Login redirect (all modes) now goes to /workspaces
- Workspace tree API filters by active workspace_id (no leak)
- Workspace name in sidebar from cookie (active_ws_name)
- Sidebar workspace section: 📄 new page + 📁 new folder buttons
- deleteWorkspacePage() in sidebar with confirmation
- _load_workspace_pages() helper with workspace_id filter
- CSS for sidebar-item-delete button (× on hover)

app/routers/auth.py

@@ -99,7 +99,7 @@ async def login(request: Request, provider: str = Query("gitea")):
                 user = conn.execute("SELECT * FROM users WHERE login='admin'").fetchone()
         user_data = dict(user)
         session = SessionManager.create_session(user_data)
-        response = RedirectResponse(url="/", status_code=302)
+        response = RedirectResponse(url="/workspaces", status_code=302)
         response.set_cookie("flowdeck_session", session, httponly=True, max_age=86400 * 7, samesite="lax")
         return response
 
@@ -265,7 +265,7 @@ async def callback(
 
     # Create session
     session = SessionManager.create_session(user_data)
-    response = RedirectResponse(url="/", status_code=302)
+    response = RedirectResponse(url="/workspaces", status_code=302)
     response.set_cookie("flowdeck_session", session, httponly=True, max_age=86400 * 7, samesite="lax")
     return response