docs: add VitePress documentation site

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- Support bilingual (English/Chinese) documentation
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docs/features/api-settings.md

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+# API Settings
+
+## One-Liner
+
+**API Settings manages AI model endpoint configuration** — Centralizes API keys, base URLs, and model selection for all supported AI backends.
+
+---
+
+## Configuration Locations
+
+| Location | Scope | Priority |
+|----------|-------|----------|
+| `~/.claude/cli-tools.json` | Global | Base |
+| `.claude/settings.json` | Project | Override |
+| `.claude/settings.local.json` | Local | Highest |
+
+---
+
+## Supported Backends
+
+| Backend | Type | Models |
+|---------|------|--------|
+| **Gemini** | Builtin | gemini-2.5-flash, gemini-2.5-pro |
+| **Qwen** | Builtin | coder-model |
+| **Codex** | Builtin | gpt-4o, gpt-4o-mini |
+| **Claude** | Builtin | claude-sonnet, claude-haiku |
+| **OpenCode** | Builtin | opencode/glm-4.7-free |
+
+---
+
+## Configuration Example
+
+```json
+// ~/.claude/cli-tools.json
+{
+  "version": "3.3.0",
+  "tools": {
+    "gemini": {
+      "enabled": true,
+      "primaryModel": "gemini-2.5-flash",
+      "secondaryModel": "gemini-2.5-flash",
+      "tags": ["analysis", "debug"],
+      "type": "builtin"
+    },
+    "codex": {
+      "enabled": true,
+      "primaryModel": "gpt-4o",
+      "tags": [],
+      "type": "builtin"
+    }
+  }
+}
+```
+
+---
+
+## Environment Variables
+
+```bash
+# API Keys
+LITELLM_API_KEY=your-api-key
+LITELLM_API_BASE=https://api.example.com/v1
+LITELLM_MODEL=gpt-4o-mini
+
+# Reranker (optional)
+RERANKER_API_KEY=your-reranker-key
+RERANKER_API_BASE=https://api.siliconflow.cn
+RERANKER_PROVIDER=siliconflow
+RERANKER_MODEL=BAAI/bge-reranker-v2-m3
+```
+
+---
+
+## Model Selection
+
+### Via CLI Flag
+
+```bash
+ccw cli -p "Analyze code" --tool gemini --model gemini-2.5-pro
+```
+
+### Via Config
+
+```json
+{
+  "tools": {
+    "gemini": {
+      "primaryModel": "gemini-2.5-flash",
+      "secondaryModel": "gemini-2.5-pro"
+    }
+  }
+}
+```
+
+---
+
+## Related Links
+
+- [CLI Call](/features/cli) - Command invocation
+- [System Settings](/features/system-settings) - System configuration
+- [CodexLens](/features/codexlens) - Code indexing