fix(vector): address PR review round 12 — bool guard + strict doc_id validation

- _group_int_doc_ids: use type(value) is not int instead of isinstance,
  since bool is an int subclass and would otherwise stringify to
  "True"/"False" and corrupt legacy payloads on backfill.
- Replace doc_id.isdigit() guards in 5 boundary sites
  (api/visualization, auth/viz_routes, search/context note/news_item/
  deck_card branches) with a shared is_valid_nextcloud_doc_id helper
  that rejects "0", leading zeros, and Unicode digit classes
  (superscripts, Arabic-Indic, Devanagari) which pass isdigit() but
  cannot be valid MySQL AUTO_INCREMENT IDs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/vector/qdrant_client.py

@@ -204,12 +204,14 @@ def _group_int_doc_ids(points: list[Any]) -> tuple[dict[str, list[Any]], int]:
         value = payload.get("doc_id")
         if value is None or isinstance(value, str):
             continue
-        if not isinstance(value, int):
-            # Producers only ever write int or str; anything else is a
-            # producer bug. Stringifying e.g. a float would write "3.0",
-            # which producers (str(int)) and the keyword index would
-            # never match, and which int() on the verification side
-            # would later reject. Skip and log loudly instead.
+        # Strict type check: bool is a subclass of int in Python, so an
+        # `isinstance(value, int)` guard would let `True`/`False` slip
+        # through and be stringified to `"True"`/`"False"` — which the
+        # keyword index would never match and the verification side
+        # would later reject. Producers only ever write int or str;
+        # anything else (bool, float, etc.) is a producer bug. Skip
+        # and log loudly instead.
+        if type(value) is not int:
             logger.warning(
                 "Unexpected doc_id type %s on point %s; skipping rewrite",
                 type(value).__name__,