feat(db): add embedded auto-migrating schema system

Replace 4 independent schema management code paths (Docker shell
script, setup wizard pg_restore, test helpers, manual psql) with a
single migration runner embedded in the server binary.

The new server/migrations/ package uses Go embed to bundle all SQL
schemas. On startup, Migrate() creates a schema_version tracking
table, detects existing databases (auto-marks baseline as applied),
and runs pending migrations in transactions.

Key changes:
- Consolidated init.sql + 9.2-update + 33 patches into 0001_init.sql
- Setup wizard simplified to single "Apply schema" checkbox
- Test helpers use migrations.Migrate() instead of pg_restore
- Docker no longer needs schema volume mounts or init script
- Seed data (shops, events, gacha) embedded and applied via API
- Future migrations just add 0002_*.sql files — no manual steps

main.go

@@ -16,6 +16,7 @@ import (
 	"erupe-ce/server/channelserver"
 	"erupe-ce/server/discordbot"
 	"erupe-ce/server/entranceserver"
+	"erupe-ce/server/migrations"
 	"erupe-ce/server/setup"
 	"erupe-ce/server/signserver"
 	"strings"
@@ -154,6 +155,16 @@ func main() {
 
 	logger.Info("Database: Started successfully")
 
+	// Run database migrations
+	applied, migErr := migrations.Migrate(db, logger.Named("migrations"))
+	if migErr != nil {
+		preventClose(config, fmt.Sprintf("Database migration failed: %s", migErr.Error()))
+	}
+	if applied > 0 {
+		ver, _ := migrations.Version(db)
+		logger.Info(fmt.Sprintf("Database: Applied %d migration(s), now at version %d", applied, ver))
+	}
+
 	// Pre-compute all server IDs this instance will own, so we only
 	// delete our own rows (safe for multi-instance on the same DB).
 	var ownedServerIDs []string