feat(db): federation schema (grants/peers/audit_log) [FED-M2-01]

Adds Drizzle ORM schema and migration for federation v1 milestone 2:

- New enums: peer_state ('pending'|'active'|'suspended'|'revoked'),
  grant_status ('active'|'revoked'|'expired')
- New tables: federation_peers, federation_grants, federation_audit_log
- FK cascades: user delete cascades grants; peer delete set-nulls audit_log
- Migration: 0008_careless_lake.sql
- Integration tests (FEDERATED_INTEGRATION=1): 6/6 pass

No business logic, no services, no DTOs — schema only.

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

packages/db/drizzle/meta/_journal.json

@@ -57,6 +57,13 @@
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       "breakpoints": true
+    },
+    {
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+      "version": "7",
+      "when": 1776821378331,
+      "tag": "0008_careless_lake",
+      "breakpoints": true
     }
   ]
-}
+}