feat: add filesystem navigation commands (/cd, /ls, /pwd, /new)

[huanglx27]

Summary

This PR adds four Unix-style filesystem commands to the IM interface (Telegram/QQ) to allow dynamic directory navigation and session management:

• /pwd: Show the current working directory.
• /cd <path>: Change the current working directory (supports ~, absolute, and relative paths).
• /ls [path]: List directory contents (with emoji indicators for dirs/files).
• /new: Clear session history and start fresh in the current directory.

Technical Changes

• Added a thread-safe cwd map to the Lazycoding struct to track per-conversation working directories.
• Updated dispatch and sessionKey to use the dynamic currentDir() instead of static configuration.
• Added a full implementation of /cd with path validation and /ls with formatted output.
• Included unit tests in internal/lazycoding/lazycoding_test.go.

Test plan

• Verified /pwd returns the initial work directory.
• Verified /cd successfully changes the path and /pwd reflects it.
• Verified /ls correctly lists and formats files/directories.
• Verified /new resets the Claude session while maintaining the current cd location.
• Ran go test ./internal/lazycoding/... - All tests passed.

🤖 Generated with Claude Code