feat(timeline): one record of what happened to the infrastructure, newest first (#6348)

A stored log, timeline_entries, with one row per thing that happened. Each
source writes its row in the same transaction as its own record, so the
history outlives the 30/90/365-day retention of the tables it points to:

- alert events (core/alerts._add_event): fired, resolved, acknowledged,
  went silent, readings back;
- finished Ansible runs (executor, and the startup sweep of interrupted
  runs): changed something, changed nothing, failed, dry run;
- audit rows (core/audit.log_audit): Steward's settings, users and access,
  sign-ins, backups. Actions another writer records are left to it.

Entries carry a kind (fixed) and an area (Service, Host OS, Hardware,
Storage, Network, Security, Monitoring). Settings → Timeline edits the
areas and each type's area and visibility; both are applied when the
timeline is read, so a change re-sorts past entries and a hidden type
comes back when shown. Kept forever unless a retention is set.

The first start fills the timeline from the last 90 days of records once,
skipping any already covered. A host rename carries its entries.

UI: Timeline in the sidebar (filter by host, area, kind; scrolls on), a
History card on each host page. MCP: get_timeline.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/hosts/routes.py

@@ -13,6 +13,7 @@ from steward.models.ansible import AnsibleRun, AnsibleRunStatus
 from steward.models.hosts import Host
 from steward.models.users import UserRole
 from steward.hosts import service as host_svc
+from steward.timeline.service import carry_host_rename
 
 hosts_bp = Blueprint("hosts", __name__, url_prefix="/hosts")
 
@@ -202,6 +203,7 @@ async def update_host(host_id: str):
             # Agent and container metrics, and the rules and windows on them,
             # go by the host's name: move them with it.
             moved = await renames.carry_rename(db, renames.HOST_SOURCES, old_name, name)
+            await carry_host_rename(db, old_name, name)
     if moved:
         await audit_request("host.renamed", "host", name,
                             {"host_id": host_id, "renamed_from": old_name, "carried": moved})