docs: 重构文档结构，添加独立模块区域 (#349)

* docs: 重构文档结构，添加独立模块区域

- 新增 /modules/ 目录用于功能模块文档
- 移动 behavior-tree 从 /guide/ 到 /modules/
- 添加模块总览页面
- 更新导航栏添加"模块"入口
- 更新侧边栏：模块区域独立侧边栏
- 更新 i18n 配置支持新模块

* style(docs): 提高文字对比度

docs/en/modules/index.md

@@ -0,0 +1,54 @@
+# Modules
+
+ESEngine provides a rich set of modules that can be imported as needed.
+
+## Module List
+
+### AI Modules
+
+| Module | Package | Description |
+|--------|---------|-------------|
+| [Behavior Tree](/en/modules/behavior-tree/) | `@esengine/behavior-tree` | AI behavior tree with visual editor |
+| [State Machine](/en/modules/fsm/) | `@esengine/fsm` | Finite state machine for character/AI states |
+
+### Gameplay
+
+| Module | Package | Description |
+|--------|---------|-------------|
+| [Timer](/en/modules/timer/) | `@esengine/timer` | Timer and cooldown system |
+| [Spatial](/en/modules/spatial/) | `@esengine/spatial` | Spatial queries, AOI management |
+| [Pathfinding](/en/modules/pathfinding/) | `@esengine/pathfinding` | A* pathfinding, NavMesh navigation |
+
+### Tools
+
+| Module | Package | Description |
+|--------|---------|-------------|
+| [Blueprint](/en/modules/blueprint/) | `@esengine/blueprint` | Visual scripting system |
+| [Procgen](/en/modules/procgen/) | `@esengine/procgen` | Noise functions, random utilities |
+
+### Network
+
+| Module | Package | Description |
+|--------|---------|-------------|
+| [Network](/en/modules/network/) | `@esengine/network` | Multiplayer game networking |
+
+## Installation
+
+All modules can be installed independently:
+
+```bash
+# Install a single module
+npm install @esengine/behavior-tree
+
+# Or use CLI to add to existing project
+npx @esengine/cli add behavior-tree
+```
+
+## Platform Compatibility
+
+All modules are pure TypeScript and compatible with:
+
+- Cocos Creator 3.x
+- Laya 3.x
+- Node.js
+- Browser