[Feature]: Calendar Integration (RFC 5545 iCal Feed & Google/Outlook Sync)

[espdesign]

Summary

Enable members to synchronize their assigned tasks and deadlines with external personal calendar applications (Google Calendar, Microsoft Outlook, Apple Calendar) via standard RFC 5545 iCalendar (webcal://) feeds and cloud calendar sync.

Background & Context

As documented in ADR-0002 and early project roadmap planning, team members frequently request viewing their due dates directly on their personal or work calendars without having to navigate Discord channels.

Proposed Capabilities

1. Subscribed iCal Feed (webcal://):
   • Unique, token-protected calendar URL per user (e.g., /api/v1/calendar/feed/{user_token}.ics).
   • Generates standard RFC 5545 VEVENT / VTODO entries for all active tasks assigned to the member.
   • Includes task title, due date, project prefix, short ID, description, priority, and direct jump URL back to the Discord thread.
2. Project-Level Calendar Feed:
   • Subscribed feed for all tasks within a given Project container for high-level milestone and release tracking.
3. External Sync Hooks:
   • Architecture prepared for 2-way sync integration via Google Calendar API and Microsoft Graph API.

Acceptance Criteria

• Members can generate or revoke a personal iCal feed URL via /pm settings calendar or API.
• Feed emits valid RFC 5545 formatted .ics streams with proper timezone conversions (UTC / user preference).
• Completing or rescheduling a task in Discord updates the calendar feed automatically.
• Feed URL contains a cryptographically secure token that can be regenerated on demand.