feat(19-01): update schema with reference item model and tags tables

- Add globalItemId and purchasePriceCents columns to items table
- Add globalItemId column to threadCandidates table
- Add tags and globalItemTags tables for tag system
- Remove itemGlobalLinks table (replaced by direct FK)
- Generate migration with data migration step before table drop

drizzle-pg/meta/_journal.json

@@ -15,6 +15,13 @@
       "when": 1775386658636,
       "tag": "0001_tough_boomerang",
       "breakpoints": true
+    },
+    {
+      "idx": 2,
+      "version": "7",
+      "when": 1775413526643,
+      "tag": "0002_wakeful_vermin",
+      "breakpoints": true
     }
   ]
 }