fix(security): redact credential-bearing URLs and PII from logs (#4750)

* fix(security): redact credential-bearing URLs and PII from logs

Several log statements emitted sensitive data in clear text:

- model_routes / chat_routes / contacts_routes logged endpoint URLs raw.
  Admin-configured URLs can embed credentials in userinfo or query
  (e.g. https://user:pass@host, ?api_key=...). Route them through a
  shared core.log_safety.redact_url() that drops userinfo/query/fragment.
- note_routes / task_scheduler logged operator email addresses (smtp_user,
  recipient). Replaced with presence booleans, which keeps the diagnostic
  ("why didn't this send") without writing PII to logs.

model_routes already had a local redactor on its HTTPStatusError branch;
the generic except branch was missed, so reuse the existing helper there.

Clears CodeQL py/clear-text-logging-sensitive-data alerts 264, 317, 324,
325, 343, 344, 528.

* fix(security): re-bracket IPv6 hosts and single-source the URL redactor

Address review on #4750:
- redact_url now re-brackets IPv6 literals so host:port stays
  unambiguous (https://[2001:db8::1]:8443/v1, not the bracket-less
  ambiguous form).
- point model_routes._redact_url_for_log at the shared helper so the
  two redactors are single-sourced (also picks up the IPv6 fix).

routes/contacts_routes.py

@@ -18,6 +18,7 @@ from pathlib import Path
 from datetime import datetime
 from urllib.parse import urljoin, urlparse, urlunparse
 
+from core.log_safety import redact_url
 from fastapi import APIRouter, Query, Depends, Response, HTTPException
 from typing import List, Dict, Optional
 
@@ -702,7 +703,7 @@ def _delete_contact(uid: str) -> bool:
                 logger.warning(
                     f"CardDAV DELETE reported success for {uid} "
                     f"but UID still present after re-fetch — "
-                    f"resource URL may differ from {url}"
+                    f"resource URL may differ from {redact_url(url)}"
                 )
                 return False
             if r.status_code == 404: