fix: note-tool timeout (background RAG indexing) + feature-flag raw-key display (#252)

- note timeout: JournalService.add_entry awaited RAG indexing inline (despite its
  "non-blocking" comment); indexing embeds via Ollama, which is CPU-bound, so
  under concurrent load it slowed enough to time the `note` gateway tool out.
  The entry is already committed before indexing, so it's best-effort — schedule
  it fire-and-forget (_schedule_rag_index) so the write returns immediately.
  A new drain_rag_index_tasks() helper lets tests await the pending index.

- feature flags: the "Gateway-health recovery" toggle rendered its raw key
  `gateway_health_enabled` (the only flag with no human description). Added the
  blurb and changed the fallback to render nothing rather than leak a raw key.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/integration/test_journal_service.py

@@ -35,7 +35,7 @@ from roboco.models.journal import (
     StruggleEntryParams,
     TaskReflectionParams,
 )
-from roboco.services.journal import JournalService
+from roboco.services.journal import JournalService, drain_rag_index_tasks
 from sqlalchemy import select, update
 from sqlalchemy.exc import IntegrityError as _IE
 
@@ -505,6 +505,7 @@ async def test_create_entry_learning_calls_record_learning(
         )
     )
     assert entry is not None
+    await drain_rag_index_tasks()  # indexing is fire-and-forget; let it run
     mock_optimal.record_learning.assert_awaited()