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

docs/architecture.md

@@ -68,6 +68,28 @@ Package dependency root:
 packages/flame_lua_runtime/assets/runtime/lua
 ```
 
+### Multi-package loading
+
+The runtime supports loading multiple packages in sequence, with module merging:
+
+```text
+RuntimeOptions.basePackages = ['_framework']
+  -> load _framework package (modules: app, diff, ids, net, ...)
+  -> load game package (modules: state, rules, main, ...)
+  -> merge into flat _moduleScripts map
+  -> game modules override framework modules on name collision
+  -> execute game entry script
+```
+
+Key classes:
+
+- `RuntimeOptions.basePackages` — ordered list of framework package IDs.
+- `PackageActivationController._prepareCandidate()` — loads base packages first, then game package, passes combined list to `ScriptEngine.loadPackages()`.
+- `LuaDardoScriptEngine.loadPackages()` — iterates all packages, merges `manifest.modules` into `_moduleScripts`, executes entry from last package.
+- `GamePackageManifest.base` — optional metadata field declaring framework dependency.
+
+Module resolution is flat: `runtime.import("xxx")` looks up `_moduleScripts[xxx]`. Game modules and framework modules share the same namespace. Later-loaded packages win on collision.
+
 ## Safety model
 
 - Lua module loading is manifest-declared.