fix(editor): repair block identity for template pages (duplicate/reordered lines)

Template-created pages (weekly report, project doc, meeting notes, to-do
list, ...) were persisted without block ids. The editor assigned ids
client-side, but the realtime room loaded the raw id-less content and sent
it back on 'sync'; applySync then merged id-less server blocks with local
blocks, producing data-bid='undefined' collisions and duplicated/shuffled
lines as soon as the user edited. Editing an empty page was unaffected
because the server state was empty.

Fixes:
- board.use_page_template: materialize unique block ids (recursively) when
  instantiating built-in or user templates.
- realtime_server: unique block_id() (uuid) + ensure_block_ids() on room
  load and on insert ops.
- editor: recursive ensureBlockIds() in init; gtTok() now restores
  [[fddate:...]] tokens (date chips survived as labels before).
- realtime client: applySync() normalizes ids, no longer appends unknown
  local blocks (duplication), and keeps local content when server is empty.

Tests: pytest (templates + realtime) and Playwright e2e covering to-do
list, weekly report date chip, Enter ordering and legacy id-less repair.

app/routers/board.py

@@ -42,6 +42,25 @@ def _ensure_page_editable(conn, page_id: int, user: dict | None) -> None:
     raise HTTPException(423, "Page is locked — only the owner of the lock or an admin can edit")
 
 
+def _ensure_block_ids(blocks) -> None:
+    """Assign unique ids to blocks missing one, recursively.
+
+    Built-in page templates ship without ids (the editor used to assign them
+    client-side only). Without persisted ids, the realtime layer and the editor
+    disagree on block identity, which duplicated lines / shuffled blocks when
+    editing a template-created page. We now materialize ids at creation time.
+    """
+    import uuid
+    if not isinstance(blocks, list):
+        return
+    for b in blocks:
+        if isinstance(b, dict):
+            if not b.get("id"):
+                b["id"] = "b" + uuid.uuid4().hex[:12]
+            if isinstance(b.get("children"), list):
+                _ensure_block_ids(b["children"])
+
+
 @router.get("/api/wiki/pages")
 async def wiki_page_search(request: Request, q: str = Query(default="")):
     """v5.11.0: page picker for [[ wiki-links. Fuzzy-ish title search across
@@ -274,9 +293,11 @@ async def use_page_template(request: Request, template_id: int):
         if body_ws:
             ws_key = body_ws
     try:
-        json.loads(blocks_json)
+        parsed_blocks = json.loads(blocks_json)
     except (json.JSONDecodeError, TypeError):
         raise HTTPException(500, "Template content corrupted") from None
+    _ensure_block_ids(parsed_blocks)
+    blocks_json = json.dumps(parsed_blocks)
     with get_conn() as conn:
         if ws_id is not None:
             next_order = conn.execute(