feat: v5.14.0 Synced blocks - block created once, edited everywhere

- Table synced_blocks (source of truth) + page_synced_blocks (references)
- Migration 15 + service app/services/synced_blocks.py
- API endpoints: CRUD synced blocks, add/remove page references
- Editor: /synced slash command, synced block rendering with badge
- Realtime: _propagate_synced broadcasts updates to all referencing rooms
- Export: synced blocks resolved in Markdown/HTML/PDF
- 18 tests in tests/test_v514_synced_blocks.py

Co-authored-by: FlowDeck <[email protected]>

app/services/realtime_server.py

@@ -304,10 +304,33 @@ class RealtimeManager:
             return
 
     async def room_state(self, page_id: int) -> dict:
-        room = self.room(page_id)
+        room = self._rooms.get(page_id)
         if not room.conns and not room.blocks:
             await self.load_room(room)
         return {"blocks": room.blocks, "title": room.title, "version": room.version}
 
+    async def _propagate_synced(self, synced_id: int) -> None:
+        """Broadcast a synced-block update to all rooms that reference it."""
+        from app.db import get_conn as _get_conn
+        # Find all pages that reference this synced block
+        pages: list[int] = []
+        try:
+            with _get_conn() as conn:
+                rows = conn.execute(
+                    "SELECT page_id FROM page_synced_blocks WHERE synced_block_id=?",
+                    (synced_id,),
+                ).fetchall()
+                pages = [r["page_id"] for r in rows]
+        except Exception:
+            return
+        for pid in pages:
+            room = self._rooms.get(pid)
+            if room and room.conns:
+                # Re-load the page content from DB to get fresh synced blocks
+                await self.load_room(room)
+                await self._broadcast(room, {"t": "synced_update",
+                                               "synced_id": synced_id,
+                                               "version": room.version})
+
 
 manager = RealtimeManager()