feat(observability): backfill logging for upload, auth, and domain services

Why:
- resolve_auth_context() runs on every authenticated request and logged
  nothing; four distinct rejection reasons (malformed/unknown/inactive/
  expired key, inactive tenant) were all invisible.
- The domain-allowlist rejection in upload_source_file() happens before any
  ingestion_jobs row exists, so it wasn't covered by the job-level
  ingestion.job.failed event either -- a rejected upload left zero trace.
- Four of upload_source_file()'s five failure branches (parse_failed,
  chunk_limit_exceeded, embedding_failed, index_failed) called
  _mark_job_failed(), which wrote to Postgres but never logged; only
  storage_failed and timeout had an ad-hoc logger.warning duplicated at their
  own call sites.

Changes:
- auth/service.py: auth.succeeded / auth.failed (with a reason field per
  rejection type), matching ADR-0011's own event catalog.
- domains/service.py: domain.rejected on the allowlist check;
  domain.created / domain.updated / domain.status_changed on the three
  mutations.
- files/upload.py: centralized failure logging inside _mark_job_failed
  (every failure branch already calls it, so logging there once closes all
  five branches instead of duplicating a log call at each site) as
  ingestion.job.failed; added ingestion.job.started; renamed the ad-hoc
  files.upload.succeeded to ingestion.job.completed for catalog consistency.

Impact:
- None to request/response behavior -- log events only.

tests/integration/postgres/test_domains_service_logging.py

@@ -0,0 +1,142 @@
+"""`domains/service.py` emits log events for the allowlist rejection and every
+mutation (ADR-0011). `ensure_domain_allowed` is the one that matters most: it
+runs before any `ingestion_jobs` row exists, so without its own log a rejected
+upload leaves no operational trace at all.
+"""
+
+from collections.abc import MutableMapping
+from typing import Any
+
+import pytest
+import structlog
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
+
+from src.application.domains import (
+    DomainAlreadyExistsError,
+    UnknownDomainError,
+    create_domain,
+    ensure_domain_allowed,
+    set_domain_status,
+    update_domain,
+)
+from tests.support.factories import create_tenant, create_tenant_domain
+
+pytestmark = [
+    pytest.mark.integration,
+    pytest.mark.postgres,
+    pytest.mark.asyncio(loop_scope="session"),
+]
+
+
+def _events_by_name(
+    logs: list[MutableMapping[str, Any]], name: str
+) -> list[MutableMapping[str, Any]]:
+    return [entry for entry in logs if entry.get("event") == name]
+
+
+async def test_ensure_domain_allowed_logs_nothing_when_the_domain_is_active(
+    db_session: AsyncSession,
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire")
+
+    with structlog.testing.capture_logs() as logs:
+        await ensure_domain_allowed(db_session, tenant_id=tenant.id, domain="fire")
+
+    assert _events_by_name(logs, "domain.rejected") == []
+
+
+async def test_ensure_domain_allowed_logs_rejection_for_an_unregistered_domain(
+    db_session: AsyncSession,
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire")
+
+    with structlog.testing.capture_logs() as logs, pytest.raises(UnknownDomainError):
+        await ensure_domain_allowed(db_session, tenant_id=tenant.id, domain="fier")
+
+    rejected = _events_by_name(logs, "domain.rejected")
+    assert len(rejected) == 1
+    assert rejected[0]["reason"] == "unregistered"
+    assert rejected[0]["domain"] == "fier"
+    assert rejected[0]["tenant_id"] == str(tenant.id)
+
+
+async def test_ensure_domain_allowed_logs_rejection_for_a_disabled_domain(
+    db_session: AsyncSession,
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire", status="disabled")
+
+    with structlog.testing.capture_logs() as logs, pytest.raises(UnknownDomainError):
+        await ensure_domain_allowed(db_session, tenant_id=tenant.id, domain="fire")
+
+    rejected = _events_by_name(logs, "domain.rejected")
+    assert len(rejected) == 1
+    assert rejected[0]["reason"] == "disabled"
+
+
+async def test_create_domain_emits_domain_created(
+    db_session: AsyncSession, db_sessionmaker: async_sessionmaker[AsyncSession]
+) -> None:
+    tenant = await create_tenant(db_session)
+    await db_session.commit()
+
+    with structlog.testing.capture_logs() as logs:
+        await create_domain(
+            db_sessionmaker, tenant_id=tenant.id, domain="car", display_name="Car insurance"
+        )
+
+    created = _events_by_name(logs, "domain.created")
+    assert len(created) == 1
+    assert created[0]["domain"] == "car"
+
+
+async def test_create_domain_duplicate_does_not_emit_domain_created(
+    db_session: AsyncSession, db_sessionmaker: async_sessionmaker[AsyncSession]
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire")
+    await db_session.commit()
+
+    with structlog.testing.capture_logs() as logs, pytest.raises(DomainAlreadyExistsError):
+        await create_domain(
+            db_sessionmaker, tenant_id=tenant.id, domain="fire", display_name="Fire again"
+        )
+
+    assert _events_by_name(logs, "domain.created") == []
+
+
+async def test_update_domain_emits_domain_updated(
+    db_session: AsyncSession, db_sessionmaker: async_sessionmaker[AsyncSession]
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire")
+    await db_session.commit()
+
+    with structlog.testing.capture_logs() as logs:
+        await update_domain(
+            db_sessionmaker, tenant_id=tenant.id, domain="fire", display_name="Fire & perils"
+        )
+
+    updated = _events_by_name(logs, "domain.updated")
+    assert len(updated) == 1
+    assert updated[0]["domain"] == "fire"
+
+
+async def test_set_domain_status_emits_domain_status_changed(
+    db_session: AsyncSession, db_sessionmaker: async_sessionmaker[AsyncSession]
+) -> None:
+    tenant = await create_tenant(db_session)
+    await create_tenant_domain(db_session, tenant=tenant, domain="fire")
+    await db_session.commit()
+
+    with structlog.testing.capture_logs() as logs:
+        await set_domain_status(
+            db_sessionmaker, tenant_id=tenant.id, domain="fire", status="disabled"
+        )
+
+    changed = _events_by_name(logs, "domain.status_changed")
+    assert len(changed) == 1
+    assert changed[0]["domain"] == "fire"
+    assert changed[0]["status"] == "disabled"