peek panels: load full page editor in iframe + resize handles

- Add ?embed=1 to /pages/{id} route, passes embed_mode to template
- base.html: embed-mode class hides sidebar/topbar, removes margins
- Replace peek-body content with iframe loading /pages/{id}?embed=1
  in both library.html and local_workspace.html
- Remove async content loading (now editor handles rendering)
- Add resize handle on left edge of peek panels (both library + local-ws)
  - Click without drag: closes panel
  - Click + drag horizontal: resizes panel width (300px to 90vw)
  - Width persisted in localStorage (fd_peek_width)
- 100% code reuse: editor runs same /pages/{id} with embed flag

app/routers/board.py

@@ -946,7 +946,9 @@ async def delete_page(request: Request, page_id: int):
 
 @router.get("/pages/{page_id}", response_class=HTMLResponse)
 async def view_page(request: Request, page_id: int):
-    """Render a page as HTML, or a file viewer for uploaded files."""
+    """Render a page as HTML, or a file viewer for uploaded files.
+    ?embed=1 — minimal mode for side peek (no sidebar/topbar)."""
+    embed = request.query_params.get("embed") == "1"
     from jinja2 import Environment, FileSystemLoader
     env = Environment(loader=FileSystemLoader("app/templates"))
     with get_conn() as conn:
@@ -1003,7 +1005,8 @@ async def view_page(request: Request, page_id: int):
            "page_data": page_data,
            "breadcrumb_items": nav_crumbs,
            "nav_workspace_id": page.get("workspace_id") or 0,
-           "nav_page_id": page_id}
+           "nav_page_id": page_id,
+           "embed_mode": embed}
     template = env.get_template("page_editor.html")
     response = template.render(**ctx)
     return HTMLResponse(content=response, headers={"Cache-Control": "no-store, max-age=0"})