feat(12-01): add migration 0008 for offer tier schema + idempotent push script

- Hand-write 0008_offer_tier_schema.sql: additive ALTER TABLE ADD COLUMN IF NOT EXISTS for offer_macros/offer_micros, guarded DO-block CHECK constraint on tier_letter, CREATE TABLE IF NOT EXISTS offer_tier_services + index
- Append journal entry for 0008_offer_tier_schema following the 0006 entry shape
- Add scripts/push-12-offer-tier-schema.ts: idempotent push script with PRODUCTION DEPLOY NOTE — BLOCKING step for Plan 02 (SSH+docker exec) before Wave 3 query layer

src/db/migrations/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1781442000000,
       "tag": "0006_add_tags_table",
       "breakpoints": true
+    },
+    {
+      "idx": 8,
+      "version": "7",
+      "when": 1781700000000,
+      "tag": "0008_offer_tier_schema",
+      "breakpoints": true
     }
   ]
 }