feat(14-01): add PGlite test helper and generate initial PostgreSQL migration

- Rewrite tests/helpers/db.ts to use drizzle-orm/pglite with async createTestDb()
- Generate initial migration with 13 CREATE TABLE statements in drizzle-pg/
- Add drizzle-pg to biome ignore list (generated files)
- PGlite smoke test confirms migrations apply and seed works

biome.json

@@ -7,7 +7,13 @@
 	},
 	"files": {
 		"ignoreUnknown": false,
-		"includes": ["**", "!src/client/routeTree.gen.ts", "!drizzle", "!.planning"]
+		"includes": [
+			"**",
+			"!src/client/routeTree.gen.ts",
+			"!drizzle",
+			"!drizzle-pg",
+			"!.planning"
+		]
 	},
 	"formatter": {
 		"enabled": true,