feat: multi-package loading with base framework support

- Add RuntimeOptions.basePackages for loading framework packages before game package
- Add ScriptEngine.loadPackages() for multi-package module merging
- LuaDardoScriptEngine merges modules from all packages, game overrides framework
- PackageActivationController loads base packages first, then game package
- GamePackageManifest parses optional 'base' field
- Update docs: README, quick-start, lua-package-format, architecture
- Update all test mocks with loadPackages() implementation

lib/runtime/game/flame_lua_game.dart

@@ -148,6 +148,7 @@ class FlameLuaGame extends FlameGame with PanDetector, ScrollDetector {
             resources: _createResourceManager(),
             scriptEngine: _bootstrapScriptEngine,
             audio: _createAudioManager(),
+            runtimeOptions: runtimeOptions,
             resourceManagerFactory: _createResourceManager,
             audioManagerFactory: _createAudioManager,
             scriptEngineFactory: _scriptEngineFactory,