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_auth.py

@@ -194,9 +194,6 @@ def test_config_page_update_persists_to_database(
 
 
 def test_config_page_shows_ticktick_oauth_link_when_ticktick_is_configured(
-    test_database_urls,
-    ready_location_database,
-    ready_poo_database,
     auth_database,
     monkeypatch,
 ) -> None: