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.

migrations/script.py.mako

@@ -0,0 +1,29 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+Reversible: yes  # 若不可逆必须改为 no 并在此说明原因 (架构文档 §16.2 迁移检查)
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+${imports if imports else ""}
+
+revision: str = ${repr(up_revision)}
+down_revision: str | None = ${repr(down_revision)}
+branch_labels: str | Sequence[str] | None = ${repr(branch_labels)}
+depends_on: str | Sequence[str] | None = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}