Fix CalDAV discovery for RFC 6764 compliance

[dkhalife]

• Add /.well-known/caldav endpoint (301 redirect to /dav/tasks/)
• Add auth middleware to root PROPFIND/REPORT so unauthenticated requests get 401 + WWW-Authenticate instead of 403
• Extract auth middleware into reusable variable

[Copilot]

Pull request overview

This PR updates the Go API server’s CalDAV routing to improve RFC 6764 discovery behavior and authentication responses for CalDAV clients.

Changes:

• Added /.well-known/caldav to redirect clients to the CalDAV collection at /dav/tasks/.
• Applied the auth middleware to root PROPFIND/REPORT requests to / (previously handled without auth middleware).
• Extracted auth.MiddlewareFunc() into a reusable authMiddleware variable for consistent use across routes.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
apiserver/internal/apis/caldav.go	0.00%	10 Missing ⚠️

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