fix(core): declare the claim column the migration adds

The migration adds session.claim_token, but neither the schema nor the
snapshot knew about it. Nothing breaks today because the two agree with
each other; it breaks the moment someone declares the field, because
generate then diffs against a snapshot without it and emits

    ALTER TABLE "session" ADD COLUMN "claim_token" text;

which fails on every database the migration has already run against.

Declared with no writer yet, so the schema, the snapshot and the
database say the same thing.

packages/core/migrations/meta/0009_snapshot.json

@@ -1219,6 +1219,12 @@
           "type": "text",
           "primaryKey": false,
           "notNull": false
+        },
+        "claim_token": {
+          "name": "claim_token",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": false
         }
       },
       "indexes": {
@@ -2313,4 +2319,4 @@
     "schemas": {},
     "tables": {}
   }
-}
+}