chore: release v0.6.2

[minorcell]

Release Goal

Ship v0.6.2 from dev to main with the latest tool-system refactors, subagent improvements, and documentation updates.

Summary of Notable Changes

• Refactored tool system toward Codex-style structure and removed legacy compatibility paths.
• Added/expanded subagent capabilities (spawn_agent/send_input/resume_agent/wait/close_agent) with default enablement and no-approval flow for subagent tools.
• Improved subagent observability: wait now returns structured details including last_output for parent-agent consumption.
• Removed legacy streaming-output mode and unified runtime on structured tool-use path.
• Reworked user/tool docs in Chinese, removed obsolete memory doc, and added dedicated subagent guidance.

Validation Status

• pnpm run test:tools passed (13 files / 56 tests).
• pnpm run test:core passed (5 files / 23 tests).
• pnpm run build passed.