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/conftest.py

@@ -17,18 +17,6 @@ def _make_app_alembic_config(database_url: str) -> Config:
     return config
 
 
-def _make_alembic_config(database_url: str) -> Config:
-    config = Config("alembic_location.ini")
-    config.set_main_option("sqlalchemy.url", database_url)
-    return config
-
-
-def _make_poo_alembic_config(database_url: str) -> Config:
-    config = Config("alembic_poo.ini")
-    config.set_main_option("sqlalchemy.url", database_url)
-    return config
-
-
 @pytest.fixture
 def test_database_urls(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
     app_database_path = tmp_path / "app_test.db"
@@ -61,18 +49,6 @@ def test_database_urls(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
         reset_db_caches()
 
 
-@pytest.fixture
-def ready_location_database(test_database_urls):
-    command.upgrade(_make_alembic_config(test_database_urls["location_url"]), "head")
-    return test_database_urls
-
-
-@pytest.fixture
-def ready_poo_database(test_database_urls):
-    command.upgrade(_make_poo_alembic_config(test_database_urls["poo_url"]), "head")
-    return test_database_urls
-
-
 @pytest.fixture
 def auth_database(test_database_urls, monkeypatch: pytest.MonkeyPatch):
     database_url = test_database_urls["app_url"]
@@ -84,7 +60,7 @@ def auth_database(test_database_urls, monkeypatch: pytest.MonkeyPatch):
 
 
 @pytest.fixture
-def app(ready_location_database, ready_poo_database, auth_database):
+def app(auth_database):
     yield create_app()
 
 
@@ -95,7 +71,7 @@ def client(app):
 
 
 @pytest.fixture
-def location_client(ready_location_database, ready_poo_database, auth_database):
+def location_client(auth_database):
     app_url = auth_database["app_url"]
     engine = create_engine(app_url, connect_args={"check_same_thread": False})
     fastapi_app = create_app()
@@ -105,7 +81,7 @@ def location_client(ready_location_database, ready_poo_database, auth_database):
 
 
 @pytest.fixture
-def poo_client(ready_location_database, ready_poo_database, auth_database):
+def poo_client(auth_database):
     app_url = auth_database["app_url"]
     engine = create_engine(app_url, connect_args={"check_same_thread": False})
     fastapi_app = create_app()