M1-T04: converge startup chain onto the single app DB

run_all_migrations() now adopts/initializes only the app DB and returns
{'app': ...}. app/main.py drops the location/poo readiness checks
(ensure_location_db_ready / ensure_poo_db_ready) and their imports;
ensure_runtime_dirs only provisions the app DB path; lifespan still
fail-closes on a missing/unmanaged app DB. Delete the retired
location/poo adopt scripts and the alembic_location / alembic_poo
chains. Update tests to single-DB expectations and drop the obsolete
location/poo adoption + readiness tests.

pytest 95 passed; ruff clean (pre-existing only); a fresh app DB
initialized via scripts.run_migrations contains location + poo_records.

tests/test_homeassistant_inbound.py

@@ -156,8 +156,6 @@ def test_homeassistant_publish_rejects_invalid_ticktick_content(location_client)
 
 
 def test_homeassistant_publish_poo_get_latest_publishes_latest_status(
-    ready_location_database,
-    ready_poo_database,
     auth_database,
 ) -> None:
     from fastapi.testclient import TestClient
@@ -215,8 +213,6 @@ def test_homeassistant_publish_poo_get_latest_publishes_latest_status(
 
 
 def test_homeassistant_publish_returns_internal_error_for_unknown_poo_action(
-    ready_location_database,
-    ready_poo_database,
     auth_database,
 ) -> None:
     from fastapi.testclient import TestClient