Support desktop-only communication channel

[pmbstyle]

Summary

• Add desktop as a supported desktop installer communication channel.
• Default the desktop setup wizard to Desktop chat and make Telegram/WhatsApp optional when that mode is selected.
• Start Octopal with Octo + gateway only for desktop-channel configs, without Telegram polling or WhatsApp bridge startup.
• Keep CLI configure limited to Telegram and WhatsApp while allowing existing desktop configs to load safely.
• Update status/dashboard/tool channel metrics and tests for the new channel.

Why

Desktop users should be able to use Octopal through the built-in desktop chat without configuring Telegram or WhatsApp first. The previous flow treated external channels as required and also mapped non-WhatsApp runtime status back to Telegram.

Validation

• npm run typecheck in desktop
• npm run build in desktop
• uv run pytest tests/test_state_active_channel.py tests/test_settings_config_sync.py tests/test_gateway_status_tool.py
• uv run ruff check src/octopal/channels/__init__.py src/octopal/cli/configure.py src/octopal/cli/main.py src/octopal/gateway/dashboard.py src/octopal/tools/catalog.py tests/test_settings_config_sync.py tests/test_state_active_channel.py