feat: add SQLite support, setup wizard enhancements, and live dashboard

Add zero-dependency SQLite mode so users can run Erupe without
PostgreSQL. A transparent db.DB wrapper auto-translates PostgreSQL
SQL ($N placeholders, now(), ::casts, ILIKE, public. prefix,
TRUNCATE) for SQLite at runtime — all 28 repo files use the wrapper
with no per-query changes needed.

Setup wizard gains two new steps: quest file detection with download
link, and gameplay presets (solo/small/community/rebalanced). The API
server gets a /dashboard endpoint with auto-refreshing stats.

CI release workflow now builds and pushes Docker images to GHCR
alongside binary artifacts on tag push.

Key changes:
- common/db: DB/Tx wrapper with 6 SQL translation rules
- server/migrations/sqlite: full SQLite schema (0001-0005)
- config: Database.Driver field ("postgres" or "sqlite")
- main.go: SQLite connection with WAL mode, single writer
- server/setup: quest check + preset selection steps
- server/api: /dashboard with live stats
- .github/workflows: Docker in release, deduplicate docker.yml

config/config.go

@@ -231,8 +231,12 @@ type Course struct {
 	Enabled bool
 }
 
-// Database holds the postgres database config.
+// Database holds the database config.
+// Driver can be "postgres" (default) or "sqlite".
+// When Driver is "sqlite", only Database (file path) is used;
+// Host, Port, User, and Password are ignored.
 type Database struct {
+	Driver   string // "postgres" or "sqlite"
 	Host     string
 	Port     int
 	User     string
@@ -454,7 +458,8 @@ func registerDefaults() {
 		{Name: "EXRenewing", Enabled: true},
 	})
 
-	// Database (Password deliberately has no default)
+	// Database (Password deliberately has no default for postgres)
+	viper.SetDefault("Database.Driver", "postgres")
 	viper.SetDefault("Database.Host", "localhost")
 	viper.SetDefault("Database.Port", 5432)
 	viper.SetDefault("Database.User", "postgres")