feat(04-07): migrate list_items.rank to COLLATE utf8mb4_bin (LIST-03)

- Add varcharBin customType helper emitting varchar(255) COLLATE utf8mb4_bin
- Replace listItems.rank varchar with varcharBin to carry explicit binary collation
- Generate migration 0002_yielding_mattie_franklin.sql: ALTER TABLE list_items
  MODIFY COLUMN rank varchar(255) COLLATE utf8mb4_bin NOT NULL (additive, no DROP)
- Apply migration via db:migrate (never db:push, per project memory constraint)
- utf8mb4_bin ensures uppercase-prefixed ranks (e.g. Zz) sort before lowercase
  ranks (e.g. a0) in DB ORDER BY, matching JS string order — closes LIST-03 gap

apps/api/src/db/migrations/0002_yielding_mattie_franklin.sql

@@ -0,0 +1 @@
+ALTER TABLE `list_items` MODIFY COLUMN `rank` varchar(255) COLLATE utf8mb4_bin NOT NULL;

apps/api/src/db/schema.ts

@@ -10,8 +10,20 @@ import {
   boolean,
   index,
   unique,
+  customType,
 } from 'drizzle-orm/mysql-core'
 
+// Custom varchar type with explicit binary collation.
+// Drizzle 0.45.x does not expose a first-class collation option on varchar,
+// so we use customType to emit `varchar(255) COLLATE utf8mb4_bin`.
+// utf8mb4_bin is required for fractional-indexing rank keys: uppercase-prefixed
+// ranks (e.g. 'Zz') must sort BEFORE lowercase ranks (e.g. 'a0') — matching JS
+// string order — so that drag-to-top persists across a DB ORDER BY rank.
+const varcharBin = (name: string) =>
+  customType<{ data: string; driverData: string }>({
+    dataType: () => 'varchar(255) COLLATE utf8mb4_bin',
+  })(name)
+
 // ── Phase 4: List tables ───────────────────────────────────────────────────
 // Imported by test/setup.ts for afterEach cleanup — keep exports consistent.
 
@@ -228,7 +240,7 @@ export const listItems = mysqlTable(
       .references(() => lists.id, { onDelete: 'cascade' }),
     text: varchar('text', { length: 500 }).notNull(),
     checked: boolean('checked').default(false).notNull(),
-    rank: varchar('rank', { length: 255 }).notNull(), // fractional-indexing string (D-13)
+    rank: varcharBin('rank').notNull(), // fractional-indexing string (D-13) — COLLATE utf8mb4_bin
     createdAt: timestamp('created_at').defaultNow().notNull(),
     updatedAt: timestamp('updated_at').defaultNow().onUpdateNow(),
   },