Add calendar integrations and collaboration updates

docs/TASKS/content/006-content-activity-endpoint.md

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+# Task: Add content activity endpoint
+
+## Feature
+
+`docs/FEATURES/production-workflow.md`
+
+## Goal
+
+Add a content-owned activity history endpoint that is separate from user-facing notifications.
+
+## Scope
+
+- Add persisted content activity entries.
+- Add `GET /api/content-items/{id}/activity`.
+- Log content creation, revisions, status changes, comments, linked assets, and asset revisions.
+- Include field-level metadata for content revision changes such as title, message, channels, hashtags, and publish date.
+- Persist publish date changes sent from the content editor revision flow.
+- Use the activity endpoint from the content detail production activity tab.
+
+## Out Of Scope
+
+- Full diff rendering UI.
+- Deleting tags or assets.
+- Notification recipient behavior changes.
+
+## Validation
+
+```bash
+dotnet build backend/Socialize.slnx
+cd frontend
+npm run build
+```
+
+## Acceptance Criteria
+
+- [x] `GET /api/content-items/{id}/activity` returns content history for users who can review the content item.
+- [x] Activity entries are not filtered by notification recipients.
+- [x] Content revision activity records changed fields.
+- [x] Publish date changes are saved and included in content activity.
+- [x] The content detail activity tab reads from content activity instead of notifications.