Add Google Calendar Tool (OneCLI-native)

This skill wires @cocal/google-calendar-mcp into selected agent groups. The MCP server reads stub credentials containing the onecli-managed placeholder; the OneCLI gateway intercepts outbound calls to calendar.googleapis.com / oauth2.googleapis.com and swaps the bearer for the real OAuth token from its vault.

Why this package (and not gongrzhe's): @gongrzhe/server-calendar-autoauth-mcp only supports the primary calendar and exposes 5 tools (no list_calendars). @cocal/google-calendar-mcp explicitly supports multi-calendar and multi-account, and is actively maintained.

Tools exposed (surfaced as mcp__calendar__<name>, exact set depends on version — run tools/list against the MCP server to enumerate): list-calendars, list-events, search-events, create-event, update-event, delete-event, get-event, list-colors, get-freebusy, get-current-time, plus multi-account management tools.

Why this pattern: v2's invariant is that containers never receive raw API keys (CHANGELOG 2.0.0). Same stub pattern /add-gmail-tool uses. This skill is deliberately a sibling, not a combined "Google Workspace" skill — installs independently and removes cleanly.

Phase 1: Pre-flight

Verify OneCLI has Google Calendar connected

onecli apps get --provider google-calendar

Expected: "connection": { "status": "connected" } with scopes including calendar.readonly and calendar.events.