Add alembic.ini missing from decoupling branch

Was present on main but never carried over. Without it, alembic
upgrade head fails with 'No script_location key found'.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic.ini

@@ -0,0 +1,35 @@
+[alembic]
+script_location = alembic
+sqlalchemy.url =
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s