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

README.md

@@ -19,6 +19,7 @@ It is designed for Flutter apps that want to host Lua-authored 2D games or inter
 - Runtime commands for movement, fading, scaling, rotation, sequencing, audio, resources, toast, clipboard, and Spine animation.
 - Shared Lua helper modules under `assets/runtime/lua/`.
 - Configurable Runtime Lua asset root via `RuntimeOptions.runtimeLuaRoot`.
+- Multi-package loading: shared framework packages loaded once, game packages loaded on top.
 
 ## Example
 
@@ -59,6 +60,18 @@ LuaGameWidget(
 )
 ```
 
+With a shared framework package:
+
+```dart
+LuaGameWidget(
+  gameId: 'ludo',
+  runtimeOptions: const RuntimeOptions(
+    runtimeLuaRoot: 'packages/flame_lua_runtime/assets/runtime/lua',
+    basePackages: ['_framework'],
+  ),
+)
+```
+
 Your app should provide game package assets such as:
 
 ```text
@@ -105,7 +118,7 @@ For AI agents and maintainers, start with:
 - [`AGENTS.md`](AGENTS.md) — package boundaries, rules, public API, and validation commands.
 - [`docs/quick-start.md`](docs/quick-start.md) — host app integration.
 - [`docs/architecture.md`](docs/architecture.md) — Dart/Lua/Flame responsibilities.
-- [`docs/lua-package-format.md`](docs/lua-package-format.md) — manifest and Lua package rules.
+- [`docs/lua-package-format.md`](docs/lua-package-format.md) — manifest, Lua package rules, and multi-package loading.
 - [`docs/protocol.md`](docs/protocol.md) — RuntimeEvent, GameDiff, RuntimeNode, RuntimeCommand boundary.
 - [`docs/validation.md`](docs/validation.md) — checks, smoke tests, and release flow.