feat(gemini): add Gemini web adapter with minimal output

[fii6]

Summary

• add a Gemini web adapter with ask, image, new, and shared page helpers
• add a plain output mode so Gemini commands can default to minimal non-table output
• keep Gemini output intentionally compact: ask returns reply text, image returns status/file/link
• simplify image args to short flags: --rt, --st, --op, --sd
• remove gemini status, gemini read, and gemini send to keep the command surface minimal

Validation

• opencli gemini ask "Reply with exactly: EMOJI_OK"
• opencli gemini image "Generate a tiny cyan moon icon" --rt 1:1 --st icon --sd true
• npm run build