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/chat_routes.py

@@ -29,6 +29,7 @@ from routes.document_helpers import _owner_session_filter
 from core.database import SessionLocal, get_session_mode, set_session_mode
 from core.database import Session as DBSession, ChatMessage as DBChatMessage
 from core.database import Document as DBDocument, ModelEndpoint
+from core.log_safety import redact_url
 from routes.research_routes import _resolve_research_endpoint
 from routes.model_routes import _visible_models
 from routes.chat_helpers import (
@@ -930,7 +931,7 @@ def setup_chat_routes(
             if effective_do_research:
                 _r_ep, _r_model, _r_headers = _resolve_research_endpoint(sess)
                 _auth_keys = list(_r_headers.keys()) if _r_headers else []
-                logger.info(f"Research endpoint resolved: model={_r_model}, endpoint={_r_ep}, auth_keys={_auth_keys}, sess_headers_keys={list(sess.headers.keys()) if isinstance(sess.headers, dict) else type(sess.headers)}")
+                logger.info(f"Research endpoint resolved: model={_r_model}, endpoint={redact_url(_r_ep)}, auth_keys={_auth_keys}, sess_headers_keys={list(sess.headers.keys()) if isinstance(sess.headers, dict) else type(sess.headers)}")
 
                 # Clarification round: only for very short/vague queries on first research message.
                 # Skip in compare mode — each pane is a fresh session, so every one would