feat(federation): add approval_token columns to peer schema

Nullable text columns on federation_peers and peer_approval_requests.
Existing rows degrade gracefully (NULL token) per spec §5; the verification
logic landing in subsequent commits routes legacy null-token state through
the existing autoAccept gate.

packages/server/drizzle/meta/_journal.json

@@ -15,6 +15,13 @@
       "when": 1777144927946,
       "tag": "0001_complex_screwball",
       "breakpoints": true
+    },
+    {
+      "idx": 2,
+      "version": "6",
+      "when": 1777196627239,
+      "tag": "0002_peer_approval_token",
+      "breakpoints": true
     }
   ]
 }