docs: add calendar integration spec

docs/TASKS/calendar-integrations/005-user-ics-export-feed.md

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+# Task: User ICS export feed
+
+## Goal
+
+Let each user subscribe to a private `.ics` feed containing their Socialize `my work` dates.
+
+## Feature Spec
+
+- `docs/FEATURES/calendar-integrations.md`
+
+## Scope
+
+- Add backend support for user export feed tokens.
+- Generate private unguessable feed URLs that do not require login.
+- Let users enable, revoke, and regenerate their export URL.
+- Emit valid `.ics` containing only the user's `my work` dates.
+- Include assigned content, approval work, owned/created content where available, approval due dates, planned publish dates, and accessible campaign dates.
+- Exclude imported holiday and observance events by default.
+- Avoid sensitive comments or approval discussion details in exported entries.
+- Add a user settings UI for copying, revoking, and regenerating the feed URL.
+- Add backend tests for feed authorization boundary, token regeneration, and event contents.
+
+## Relevant Files
+
+- `backend/src/Socialize.Api/Modules/CalendarIntegrations/`
+- `backend/src/Socialize.Api/Modules/ContentItems/`
+- `backend/src/Socialize.Api/Modules/Approvals/`
+- `frontend/src/features/user-profile-settings/`
+- `frontend/src/config.js`
+- `backend/tests/Socialize.Tests/`
+
+## Validation
+
+```bash
+dotnet build backend/Socialize.slnx
+dotnet test backend/Socialize.slnx
+cd frontend
+npm run build
+./scripts/update-openapi.sh
+```