feat: add calendar management (read, create, schedule)

[avoidwork]

Summary

Add calendar management tools for reading events, creating/updating/deleting events, checking availability, and generating meeting summaries via Google Calendar and Outlook/MS Graph.

Motivation

Productivity workflows revolve around scheduling. The agent has no capability to interact with calendar systems — it cannot read upcoming events, create new meetings, check attendee availability, update existing events, or generate meeting summaries. This is a fundamental gap for any agent designed to assist with professional workflows. Users cannot ask the agent to "find a 30-minute slot tomorrow" or "summarize my afternoon meetings."

Proposed Solution

Create a calendar skill that provides:

• Read events: Fetch calendar events with filtering (date range, calendar, attendee, keyword)
• Create events: Schedule new meetings with title, time, attendees, location, description
• Update events: Modify existing events (time changes, attendee additions, description updates)
• Delete events: Cancel/remove events
• Check availability: Find free time slots, conflict detection
• Meeting summaries: Generate summaries of past events from calendar descriptions and attached notes
• Multi-provider support: Google Calendar API, Outlook/MS Graph API
• Timezone awareness: Proper handling of timezone conversions

Alternatives Considered

• Shell-based calendar tools (khal, calcurse): limited to local calendars, no cloud sync.
• Single-provider only (Google Calendar): excludes enterprise/Outlook users.
• Email-based scheduling: fragile, no structured data access.

OpenSpec Note

This project uses OpenSpec for feature development. If this request is approved, I will:

1. Run /opsx:propose to generate a full proposal with specs and tasks
2. Iterate on the design before any code is written
3. Follow the task-driven implementation workflow

Additional Context

This should integrate with the email gap (#779) for scheduling workflows — e.g., creating a calendar event and sending calendar invites via email simultaneously.

Audit Findings (for Issue #781)

• src/tools/index.js — Tools are registered here with TOOL_PERMISSIONS and TOOL_CLASSIFICATIONS. Calendar tools would need network:outbound permission and likely classifications for scheduling/productivity agents.
• src/tools/date.js — Existing date tool provides date awareness; calendar tools would extend this with event-level operations.
• src/config/config.js / src/config/loader.js — Calendar API credentials (OAuth tokens, API keys) would need secure storage.
• src/config/schemas/providers.js — Calendar provider configuration schemas (Google Calendar, MS Graph) would follow existing patterns.
• src/tools/web.js — Existing web tool uses network:outbound; calendar tools would follow the same permission model.
• src/agent/deepAgents.js — Agent orchestration; calendar tools would be registered alongside existing tools.
• src/scheduler/cron.js / src/scheduler/scheduler.js — Existing scheduler infrastructure; calendar tools could leverage or integrate with this for recurring event detection.
• Dependency note — Google Calendar API requires googleapis npm package. MS Graph requires @microsoft/microsoft-graph-client. OAuth flows add complexity — consider starting with API key and adding OAuth later.
• Integration point — Cross-references feat: add email integration (read, send, manage) #779 (email integration). Calendar invites should be sent via email tools. Shared auth abstraction between email and calendar tools is recommended.