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/__init__.py

@@ -0,0 +1,45 @@
+# plugins/homeassistant/__init__.py
+from __future__ import annotations
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from quart import Quart
+
+_app: "Quart | None" = None
+
+
+def setup(app: "Quart") -> None:
+    global _app
+    _app = app
+    from .models import HomeAssistantConnection, HomeAssistantUpdate  # noqa: F401 — registers the tables
+    from .timeline import register
+    register()
+
+
+def get_scheduled_tasks() -> list:
+    from .scheduler import make_tick_task
+    return [make_tick_task(_app)]
+
+
+def get_blueprint():
+    from .routes import homeassistant_bp
+    return homeassistant_bp
+
+
+def get_nav() -> list[dict]:
+    return [{"label": "Home Assistant", "href": "/plugins/homeassistant/"}]
+
+
+def get_alert_metrics() -> dict[str, list[str]]:
+    """What the poll records, all under the resource "homeassistant"."""
+    return {"homeassistant": ["is_up", "backup_age_hours", "updates_waiting"]}
+
+
+def register_mcp_tools(register) -> None:
+    from .mcp_tools import register_tools
+    register_tools(register)
+
+
+async def mcp_overview(db) -> list[dict]:
+    from .mcp_tools import mcp_overview as findings
+    return await findings(db)