feat(db): initial migration with pgvector and the eight foundation tables

Creates the vector extension plus id_user, id_user_identity, id_consent,
bl_quota_rule, bl_quota, bl_ledger, tk_task and ob_ai_call using the domain
prefixes of 架构文档 §6.1, and seeds the quota rules. Reversible: verified by
an upgrade/downgrade/upgrade round-trip, which CI now runs on every push.

alembic.ini

@@ -0,0 +1,40 @@
+[alembic]
+script_location = migrations
+prepend_sys_path = .
+path_separator = os
+# The URL is read from DATABASE_URL via packages.shared.config in migrations/env.py.
+sqlalchemy.url =
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+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
+datefmt = %H:%M:%S