Add comprehensive test coverage and WebSocket notifications for CalDAV due date updates

[Copilot]

Overview

The CalDAV API already supported updating task due dates through PUT requests with VTODO data, but lacked comprehensive test coverage and real-time notification support. This PR enhances the implementation with proper testing and real-time updates.

What's Changed

1. Added Comprehensive Test Coverage

Created parser_test.go with 6 new tests covering all due date parsing scenarios:

• Parsing VTODO with full timestamp format (DUE:20230115T120000Z)
• Parsing VTODO with date-only format (DUE:20230116)
• Parsing VTODO without due dates (nil handling)
• Updating existing due dates
• Removing due dates
• Handling empty VTODO documents

Enhanced caldav_test.go with 3 additional tests:

• Generating VTODO with due dates in correct format
• Generating VTODO without due dates (no DUE field)
• Verifying LAST-MODIFIED timestamps are updated correctly

2. Added Real-time WebSocket Notifications

Enhanced CalDAVAPIHandler to broadcast WebSocket notifications when tasks are updated via CalDAV:

// Broadcast the update to all connected clients for this user
h.ws.BroadcastToUser(currentIdentity.UserID, ws.WSResponse{
    Action: "task_updated",
    Data:   updatedTask,
})

This ensures that when a task is updated through CalDAV synchronization, all connected web clients receive real-time updates, providing a consistent experience across the REST API and CalDAV endpoints.

How It Works

When a CalDAV client updates a task's due date:

1. Client sends PUT request to /dav/tasks/{taskId}.ics with VTODO containing a DUE field
2. ParseVTODO extracts the title and due date (supports both full timestamp and date-only formats)
3. UpdateTask updates the task's NextDueDate field
4. UpsertTask persists changes (GORM automatically updates the UpdatedAt timestamp)
5. WebSocket notification broadcasts the update to all connected clients
6. Server returns HTTP 204 No Content

Supported due date formats:

• Full timestamp: DUE:20230115T120000Z
• Date only: DUE:20230116
• No due date: DUE field omitted

Testing

• ✅ All 16 test packages pass
• ✅ Application builds successfully
• ✅ 9 new tests added, all passing
• ✅ No breaking changes to existing functionality

Backward Compatibility

All changes are backward compatible. The WebSocket broadcasting is non-blocking and includes graceful error handling, so CalDAV updates will succeed even if WebSocket notifications fail.

Original prompt

Implement support for updating the next due date through the calDav API

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
apiserver/internal/apis/caldav.go	0.00%	13 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Copilot]

Pull Request Overview

This PR adds comprehensive test coverage for CalDAV due date parsing and generation functionality, while also implementing real-time WebSocket notifications when tasks are updated via the CalDAV API.

Key Changes:

• Added 6 new tests in parser_test.go covering all due date parsing scenarios (timestamp format, date-only format, nil handling, updates, and removals)
• Added 3 new tests in caldav_test.go for VTODO generation with due dates and LAST-MODIFIED timestamps
• Enhanced CalDAVAPIHandler to broadcast WebSocket notifications when tasks are updated through CalDAV

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
apiserver/internal/utils/caldav/parser_test.go	New comprehensive test suite for ParseVTODO function covering all due date scenarios
apiserver/internal/repos/caldav/caldav_test.go	Added tests for generateVTODO with due dates and timestamp verification
apiserver/internal/apis/caldav.go	Integrated WebSocket server to broadcast task updates after CalDAV PUT operations

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