feat(14-01): generate and apply Drizzle migration 0010 for multi-signer columns

- Migration 0010_sharp_archangel.sql adds signer_email to signing_tokens
- Migration adds signers JSONB column to documents
- Migration adds completion_triggered_at TIMESTAMP to documents
- Additive-only: no DROP columns, no ALTER TYPE, no backfills
- Applied successfully to local Neon/Postgres instance

teressa-copeland-homes/drizzle/meta/_journal.json

@@ -71,6 +71,13 @@
       "when": 1774126681669,
       "tag": "0009_luxuriant_catseye",
       "breakpoints": true
+    },
+    {
+      "idx": 10,
+      "version": "7",
+      "when": 1775250937545,
+      "tag": "0010_sharp_archangel",
+      "breakpoints": true
     }
   ]
 }