feat: add browser-based one-click login

[echowxsy]

Summary

Add automatic cookie capture via browser login, eliminating the need to manually extract and set LARK_COOKIE environment variable.

Features

• Browser login — Opens Feishu login page in Chromium, captures session cookies after login
• Cookie persistence — Saved to ~/.lark/msg/cookie.json for reuse across sessions
• Auto-load — Auth layer automatically loads saved cookie when LARK_COOKIE env var is not set
• CLI integration — --login / --logout / --login-timeout arguments

Usage

# First time: login via browser
python main.py --login

# Run the agent (cookie auto-loaded)
python main.py

# Clear saved cookie
python main.py --logout

Changes

• app/api/browser_login.py (new) — Playwright-based login with cookie capture and persistence
• app/api/auth.py — Add is_authenticated() check, auto-load saved cookie as fallback
• main.py — Add argparse with --login/--logout/--login-timeout flags
• requirements.txt — Add playwright>=1.40.0 (optional dependency)
• .env.example — Add comment about --login option

Test plan

• python main.py --login opens browser and captures cookie after login
• Cookie is saved to ~/.lark/msg/cookie.json
• python main.py loads saved cookie automatically
• python main.py --logout clears saved cookie
• Running without cookie shows helpful error message
• Still works with LARK_COOKIE env var (takes priority over saved file)

🤖 Generated with Claude Code