feat: wire up --version and fail gracefully without a TTY

[kunjee17]

Two small CLI gaps plus the doc update for headless/MCP.

--version

#[command(version)] was never set, so --version errored and was absent from --help. Now irona --version prints irona 0.5.0.

No-TTY failure

Bare irona in a pipe or CI job called enable_raw_mode() and died with No such device or address (os error 6). Now it checks stdin/stdout up front and exits 1 with:

irona: the interactive TUI needs a terminal, but stdin or stdout is not a TTY.
       For non-interactive use:
         irona --clean <path>   delete artifacts and print a one-line summary
         irona --mcp            run as a Model Context Protocol server over stdio

The check sits after the --mcp and --clean branches, so both headless modes still run fine without a TTY (verified by piping each).

README

• Usage section now covers all three modes with a flag table, replacing the TUI-only key list
• Fixed the stale claim that irona "scans your home directory" — it scans PATH, default .
• MCP section documents both tools' inputs and returned fields, their readOnlyHint/destructiveHint annotations, and that scan_artifacts includes gitignore-only matches (opposite of --clean's default)
• Added claude mcp add irona -- irona --mcp
• Fixed the Claude Code Stop hook example, which used a flat {"command": ...} that the real settings.json schema does not accept

Testing

83 tests pass (4 new: version flag, TTY precondition matrix, hint content). fmt and clippy clean.