docs: remove all remaining Playwright references from docs

Updated 6 files:
- CDP.md, CDP.zh-CN.md: Browser Bridge instead of Playwright MCP Bridge
- CLI-ELECTRON.md: Browser Bridge / IPage abstraction wording
- CLI-EXPLORER.md: browser tools instead of Playwright MCP tools
- TESTING.md: Browser Bridge extension mode, removed token references
- src/clis/chatgpt/README{,.zh-CN}.md: CDP instead of Playwright

Zero Playwright references remaining across all .md files.