fix: Share dialog alignment, z-index, access menu colors, shared section

- Dialog right edge aligns with Share button area (right: 72px)
- z-index raised to 999 to prevent being hidden by other layers
- Max-height reduced to 65vh to fit viewport
- Access menu: !important dark background, proper option styling
- Sidebar Shared section now renders shared_pages dynamically
- board.py: shared_pages added to _sidebar_data() return

app/routers/board.py

@@ -196,8 +196,8 @@ def _sidebar_data(request: Request, owner: str = "", repo: str = "") -> dict:
     return {"workspace_name": ws_name, "workspace_initial": ws_name[0].upper() if ws_name else "B",
             "current_page": repo or "Dashboard", "last_edited": "now",
             "recent_pages": recent, "private_pages": private_items,
-            "favorite_pages": favorites, "user": user,
-            "workspace_key": ws_key}
+            "favorite_pages": favorites, "shared_pages": [],
+            "user": user, "workspace_key": ws_key}
 
 
 def _extract_ai_keywords(owner: str, repo: str, labels: list[dict], body: str = ""):