📝 docs: simplify README + platform-agnostic tools + auto-create local rules

- Simplify docs/ section to grouped summary with pointer to docs/index.md
- Remove outdated performance metrics table
- Use cross-platform path examples throughout
- Make AGENT_RULES tool usage section platform-agnostic
- Auto-create AGENT_RULES.local.md on sync_rules (empty template)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/AGENT_RULES.template.md

@@ -192,7 +192,7 @@
 - **并行执行**：独立的工具调用尽可能并行执行
 - **遵循 schema**：严格遵循工具参数定义
 - **避免循环**：避免重复调用同一工具获取相同信息
-- **优先专用工具**：文件操作用 Read/Edit/Write，搜索用 Grep/Glob
+- **优先专用工具**：文件操作用专用文件工具（非 cat/sed），搜索用专用搜索工具（非 grep/find）
 
 ## Context 管理