[WIP] feat: Command safety classification (safe/dangerous)

[quangdang46]

Gap #15 — High

Command safety classification for auto-approval of safe commands.

Source: codex

What's needed:

• is_known_safe_command() — returns true for read-only commands (cat, ls, echo, pwd)
• command_might_be_dangerous() — returns true for destructive commands
• Composite command parsing (bash -lc "...")
• Git subcommand danger detection
• Platform-specific safe/dangerous command lists

Reference: codex codex-rs/shell-command/src/command_safety/