feat(homeassistant): its page offers the metrics scrape under the same sign-in, so one user covers everything (#6744)

A Prometheus target's token_from names the plugin that supplies its token at each
scrape. Read its metrics makes the target; Use this sign-in moves one at that address
across, keeping its name, filters and history. A refusal stops the connection, so one
Try again or sign-in starts everything, and the sign-in is only sent to its own address.
A 404 says how to turn on Home Assistant's Prometheus integration, as Steward doesn't
change Home Assistant. Refused also joins the volatile columns a backup check ignores.

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

plugins/homeassistant/mcp_tools.py

@@ -13,6 +13,7 @@ from steward.mcp.tools._shape import age_s, db_session, iso, now_utc, redact_url
 from steward.mcp.tools.overview import finding
 from steward.models.users import UserRole
 
+from . import metrics
 from .models import HomeAssistantConnection, HomeAssistantUpdate
 from .routes import connection_says
 from .service import STALE_BACKUP_HOURS, backup_age_hours, backup_verdict, installable, parse_moment
@@ -35,13 +36,16 @@ async def get_home_assistant() -> dict:
     `installable` is what update_home_assistant takes (Core, OS, add-ons);
     `others_waiting` is firmware and custom integrations, which Steward leaves
     to Home Assistant. `can_install` is whether the Home Assistant user who signed
-    Steward in is an administrator, which installing needs.
+    Steward in is an administrator, which installing needs. `metrics` is the
+    Prometheus target that reads its metrics, `uses_sign_in` saying whether that
+    same user does; null when the Prometheus plugin is off.
     """
     now = now_utc()
     async with db_session() as db:
         c = (await db.execute(select(HomeAssistantConnection))).scalars().first()
         runs = list((await db.execute(select(HomeAssistantUpdate).order_by(
             HomeAssistantUpdate.started_at.desc()).limit(RECENT_UPDATES))).scalars())
+        scrape = await metrics.state(db, c) if c else None
     if c is None:
         return {"connected": False, "says": "No connection yet: an admin signs in on the Home Assistant page."}
     reach, says = connection_says(c, now)
@@ -55,7 +59,7 @@ async def get_home_assistant() -> dict:
             "backup": {"verdict": backup_verdict(backup, now)[1], "last_ok": iso(parse_moment(backup.get("last_ok"))),
                        "age_hours": round(age, 1) if age is not None else None, "stale_after_hours": STALE_BACKUP_HOURS,
                        "next": iso(parse_moment(backup.get("next"))), "last_result": backup.get("last_result")},
-            "updates": [_run_view(r) for r in runs]}
+            "metrics": scrape, "updates": [_run_view(r) for r in runs]}
 
 
 async def update_home_assistant(entity_id: str) -> dict: