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/quick-start.md

@@ -98,3 +98,77 @@ flutter run --dart-define=LUA_GAME_ID=flight
   }
 }
 ```
+
+## Multi-package loading (base + game)
+
+When multiple games share common modules (event router, diff utilities, panel stack, network layer), extract them into a framework package and load it before the game package.
+
+Framework package structure:
+
+```text
+assets/games/_framework/
+  manifest.json
+  scripts/
+    app.lua
+    diff.lua
+    event_router.lua
+    ids.lua
+    net.lua
+    panel_stack.lua
+```
+
+Framework manifest:
+
+```json
+{
+  "gameId": "_framework",
+  "name": "Lua Game Framework",
+  "version": "1.0.0",
+  "runtimeApiVersion": 1,
+  "entry": "scripts/app.lua",
+  "assetsBase": "assets",
+  "modules": {
+    "app": "scripts/app.lua",
+    "diff": "scripts/diff.lua",
+    "event_router": "scripts/event_router.lua",
+    "ids": "scripts/ids.lua",
+    "net": "scripts/net.lua",
+    "panel_stack": "scripts/panel_stack.lua"
+  }
+}
+```
+
+Game manifest (no framework modules needed):
+
+```json
+{
+  "gameId": "ludo",
+  "base": "_framework",
+  "modules": {
+    "state": "scripts/state.lua",
+    "rules": "scripts/rules.lua",
+    "main": "scripts/main.lua"
+  }
+}
+```
+
+Game code imports framework modules transparently:
+
+```lua
+local app = runtime.import("app")       -- from framework
+local state = runtime.import("state")   -- from game
+```
+
+Embed with base packages:
+
+```dart
+LuaGameWidget(
+  gameId: 'ludo',
+  runtimeOptions: const RuntimeOptions(
+    runtimeLuaRoot: 'packages/flame_lua_runtime/assets/runtime/lua',
+    basePackages: ['_framework'],
+  ),
+)
+```
+
+Module resolution order: game package modules override framework modules with the same name. The entry script always comes from the last package (game package).