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/services/realtime_server.py

@@ -25,8 +25,26 @@ def color_for(uid: int) -> str:
 
 
 def block_id() -> str:
-    import time
-    return f"b{int(time.time()*1000)}"
+    import uuid
+    return "b" + uuid.uuid4().hex[:12]
+
+
+def ensure_block_ids(blocks: list[dict]) -> list[dict]:
+    """Assign unique ids to blocks missing one, recursively.
+
+    Template-created pages may have been persisted without block ids; without
+    them the room state is not addressable by ops and the editor ends up with
+    ``data-bid="undefined"`` blocks (duplicated / reordered lines).
+    """
+    if not isinstance(blocks, list):
+        return blocks
+    for b in blocks:
+        if isinstance(b, dict):
+            if not b.get("id"):
+                b["id"] = block_id()
+            if isinstance(b.get("children"), list):
+                ensure_block_ids(b["children"])
+    return blocks
 
 
 def apply_op(blocks: list[dict], op: dict) -> list[dict]:
@@ -37,6 +55,7 @@ def apply_op(blocks: list[dict], op: dict) -> list[dict]:
         if not blk.get("id"):
             blk = dict(blk)
             blk["id"] = block_id()
+        ensure_block_ids([blk])
         idx = op.get("index")
         if not isinstance(idx, int):
             idx = len(blocks)
@@ -126,7 +145,7 @@ class RealtimeManager:
         room.title = row["title"] or ""
         if (row["content_format"] or "") == "blocks" and row["content"]:
             try:
-                room.blocks = json.loads(row["content"])
+                room.blocks = ensure_block_ids(json.loads(row["content"]))
             except Exception:
                 room.blocks = []
         return True