fix: 500 on /pages/{id} — missing page_data in dashboard.py context

Same pattern as f7d9d91: dashboard.router is registered before board.router
in main.py, so its /pages/{id} takes priority. Added page_data dict to match
the new JSON script tag approach.

app/routers/dashboard.py

@@ -169,7 +169,8 @@ async def view_page_root(request: Request, page_id: int):
     ctx = {**sidebar, "page": page, "sub_pages": [dict(s) for s in subs],
            "page_favorited": False,
            "page_share_mode": page.get("share_mode", "private"),
-           "page_published": bool(page.get("published", 0))}
+           "page_published": bool(page.get("published", 0)),
+           "page_data": {"id": page_id, "title": page.get("title"), "content_format": page.get("content_format", "blocks"), "content": page.get("content", ""), "favorited": False, "share_mode": page.get("share_mode", "private"), "published": bool(page.get("published", 0))}}
     template = env.get_template("page_editor.html")
     response = template.render(**ctx)
     return HTMLResponse(content=response, headers={"Cache-Control": "no-store, max-age=0"})