feat: add /gentle:shy command to toggle startup role and title animation

[yuritoledo]

Summary

Adds shy mode — a per-project toggle to disable the rose startup intro, pen-writing logo animation, and runtime stats panel. Inspired by the "shy gentle pi" concept: let users who prefer a clean, quiet startup opt out without modifying the extension.

Changes

New file: lib/shy-config.ts

Shared config module providing isShyMode(), setShyMode(), and toggleShyMode(). Persists state in .pi/gentle-ai/shy.json.

Modified: extensions/startup-banner.ts

Added a isShyMode(ctx.cwd) early return at the top of the session_start handler. When shy mode is ON, the entire startup animation block is skipped — no screen clear, no ASCII art, no pen writing, no stats panel.

Modified: extensions/gentle-ai.ts

• Registers /gentle:shy, /gentle-ai:shy, and /gentleman:shy commands that toggle shy mode and notify the user.
• /gentle-ai:status now reports shy mode status (ON / OFF).

Modified: README.md

• Adds shy mode to the capabilities table.
• Adds a dedicated Shy mode section with config path example.
• Adds shy commands to the quick-start, commands table, and compatibility aliases.

Design decisions

• Off by default — existing users see no behavior change. Only those who run /gentle:shy get the silent startup.
• Project-scoped config — follows the existing .pi/gentle-ai/ pattern used by persona config.
• Three command aliases — consistent with how /gentle:persona, /gentle-ai:persona, and /gentleman:persona work.
• Status visible — /gentle-ai:status shows whether shy mode is active.
• Restart required — the change takes effect on next Pi session (consistent with persona mode).
• Minimal diff — adds 4 lines to startup-banner.ts, 35 lines to gentle-ai.ts, 33 lines of new module, README docs. No test changes needed; all 20 existing tests pass.