MM-28765: Fix errcheck issues in server/channels/manualtesting/manual_testing.go (#30613)

1. Fixed hasher.Write() to check error return
2. Fixed VerifyEmail() to check error return
3. Fixed SaveMember() to check error return
4. Added typecheck exclusion for testAutoLink in .golangci.yml

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

server/.golangci.yml

@@ -119,7 +119,6 @@ issues:
         channels/jobs/helper_test.go|\
         channels/jobs/hosted_purchase_screening/worker.go|\
         channels/jobs/jobs.go|\
-        channels/manualtesting/manual_testing.go|\
         channels/store/localcachelayer/channel_layer.go|\
         channels/store/localcachelayer/channel_layer_test.go|\
         channels/store/localcachelayer/emoji_layer.go|\