feat(01-foundation-01): Alembic migrations with RLS and tenant isolation tests

- alembic.ini + migrations/env.py: async SQLAlchemy migration setup using asyncpg
- migrations/versions/001_initial_schema.py: creates tenants, agents, channel_connections, portal_users
  - ENABLE + FORCE ROW LEVEL SECURITY on agents and channel_connections
  - RLS policy: tenant_id = current_setting('app.current_tenant', TRUE)::uuid
  - konstruct_app role created with SELECT/INSERT/UPDATE/DELETE on all tables
- packages/shared/shared/rls.py: idempotent configure_rls_hook, UUID-sanitized SET LOCAL
- tests/conftest.py: test_db_name (session-scoped), db_engine + db_session as konstruct_app
- tests/unit/test_normalize.py: 11 tests for KonstructMessage Slack normalization (CHAN-01)
- tests/unit/test_tenant_resolution.py: 7 tests for workspace_id → tenant resolution (TNNT-02)
- tests/unit/test_redis_namespacing.py: 15 tests for Redis key namespace isolation (TNNT-03)
- tests/integration/test_tenant_isolation.py: 7 tests proving RLS tenant isolation (TNNT-01)
  - tenant_b cannot see tenant_a's agents or channel_connections
  - FORCE ROW LEVEL SECURITY verified via pg_class.relforcerowsecurity

migrations/script.py.mako

@@ -0,0 +1,28 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}