feat(deploy): migrations 嵌入二进制，实现真单文件部署

- embed-migrations.ts：扫 ./drizzle/meta/_journal.json，生成 src/server/db/migrations.gen.ts，每条 SQL 通过 `import sql_<idx> from '../../../drizzle/<tag>.sql' with { type: 'text' }` 在 bun build --compile 时被静态嵌入二进制
- migrate.ts 重写：runtime 用 createHash('sha256') 计算迁移哈希，仅用 db.execute(sql) + db.transaction() 公开 API 写入 drizzle.__drizzle_migrations 簿记表（不依赖 @internal 的 db.dialect/db.session）
- db:generate 链 db:embed，保证 SQL 改动总是同步到 migrations.gen.ts
- Dockerfile 删 COPY drizzle/，binary 是部署唯一 artifact
- 同步 README / AGENTS / biome.json

src/server/db/migrations.gen.ts

@@ -0,0 +1,8 @@
+// AUTO-GENERATED by `bun run db:embed`. Do not edit.
+import sql_0 from '../../../drizzle/0000_loving_thunderbird.sql' with { type: 'text' }
+
+export type EmbeddedMigration = { tag: string; sql: string; when: number; breakpoints: boolean }
+
+export const embeddedMigrations: readonly EmbeddedMigration[] = [
+  { tag: '0000_loving_thunderbird', sql: sql_0, when: 1777096386609, breakpoints: true },
+]