test(comments): add integration tests and fix constructor signatures
Add integration tests for comment write operations testing:
- CreateComment XRPC endpoint validation
- UpdateComment authorization and validation
- DeleteComment authorization and success
Fix existing integration tests to use NewCommentServiceWithPDSFactory
with nil factory for read-only test scenarios. This allows tests that
only exercise the read path (GetComments) to work without OAuth setup.
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Co-Authored-By: Claude <noreply@anthropic.com>