fix: sidebar workspace section — hide create buttons quand aucun workspace actif

- Ajout flag has_active_workspace dans _sidebar_data (dashboard.py + board.py)
- Template base.html: quand has_active_workspace=False:
  - Titre section → '📁 No workspace open'
  - Boutons New File/New Folder cachés
  - Message 'Open a workspace to see your files'
- Guard JS newPageInWorkspace()/newFolderInWorkspace(): toast + redirect si pas de workspace
- 143 tests passent

app/routers/dashboard.py

@@ -73,8 +73,9 @@ def _sidebar_data(request: Request, repos: list[dict], include_workspace: bool =
     gitea_workspace = False
     gitea_owner = ""
     gitea_repo = ""
+    has_active_workspace = False
 
-    if include_workspace and ws_cookie and ws_cookie.startswith("gitea:"):
+    if ws_cookie and ws_cookie.startswith("gitea:"):
         # Gitea workspace: set owner/repo for client-side tree loading
         # BUT keep local workspace pages — they go in the "Private" section
         parts = ws_cookie.split(":", 2)
@@ -83,6 +84,7 @@ def _sidebar_data(request: Request, repos: list[dict], include_workspace: bool =
             gitea_repo = parts[2]
             active_ws_name = f"{gitea_owner}/{gitea_repo}"
             gitea_workspace = True
+            has_active_workspace = True
             # workspace_pages stays as-is (local tree, loaded above)
     elif include_workspace and ws_cookie and user:
         try:
@@ -96,6 +98,7 @@ def _sidebar_data(request: Request, repos: list[dict], include_workspace: bool =
                 if row:
                     active_ws_name = row["name"]
                     workspace_pages = _load_workspace_pages(ws_cookie)
+                    has_active_workspace = True
                 # else: stale cookie from another user — ignore
         except (ValueError, Exception):
             pass
@@ -169,6 +172,7 @@ def _sidebar_data(request: Request, repos: list[dict], include_workspace: bool =
         "auth_method": auth_method,
         "gitea_linked": gitea_linked,
         "github_linked": github_linked,
+        "has_active_workspace": has_active_workspace,
     }