feat(homeassistant): waiting updates, backup age, and updates installed after a confirmed backup (#6355)

A new plugin reads Home Assistant with a read-only token every 5 minutes and
shows which Core, OS and add-on updates are waiting and how old the last backup
is. Install takes a backup through a local-only webhook, confirms Home
Assistant's last-backup time moved, installs, and follows the update to its end,
through Home Assistant's and Steward's own restarts. One runs at a time. Each
ends as one timeline entry.

Steward holds nothing that can act on the house: the webhook's automation can
only take a backup or install an allowed update (System 231's ruling). A refused
token stops polling, as Home Assistant bans an address after a few refusals.

Milestone 576 steps 1 to 5.

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

plugins/homeassistant/timeline.py

@@ -0,0 +1,34 @@
+# plugins/homeassistant/timeline.py
+"""What Home Assistant maintenance puts on the timeline: each update once it ends."""
+from __future__ import annotations
+
+from steward.timeline import catalog
+from steward.timeline.record import record_or_update
+
+TYPES = (
+    ("homeassistant.updated", "Home Assistant updated", "automation", "service", True,
+     "Steward installed a Home Assistant update after a confirmed backup."),
+    ("homeassistant.update_failed", "Home Assistant update failed", "automation", "service", True,
+     "A Home Assistant update Steward was asked to install didn't finish."),
+)
+
+
+def register() -> None:
+    for t in TYPES:
+        catalog.register_type(*t)
+    from .models import HomeAssistantUpdate
+    catalog.register_ref("homeassistant_update", HomeAssistantUpdate)
+
+
+async def update_entry(session, run) -> None:
+    done = run.state == "done"
+    versions = f"{run.from_version} to {run.to_version}" if run.to_version else "a new version"
+    summary = (f"{run.title} updated from {versions}" if done
+               else f"{run.title} update failed: {run.message}")
+    await record_or_update(
+        session, ("homeassistant_update", run.id),
+        type="homeassistant.updated" if done else "homeassistant.update_failed",
+        at=run.started_at, until=run.finished_at, summary=summary, subject=run.title,
+        detail={"entity_id": run.entity_id, "from": run.from_version, "to": run.to_version,
+                "url": "/plugins/homeassistant/"},
+        actor=run.started_by or "Steward")