Fix N+1 query in Node#tagnames_as_classes

[aopv]

Summary

• Eliminates N+1 query in Node#tagnames_as_classes by replacing Node.select([:nid]).find(id).tagnames with a direct Tag.joins(:node_tag).pluck(:name) call
• Reduces two queries per node (Node.find + tag association load) to a single efficient pluck query
• No change in behavior — returns the same tag class strings used in note listing views

Details

The previous implementation re-fetched the node via Node.find(id) to bypass a potentially filtered tag association (caused by joins in the calling context). This created an N+1 problem when rendering lists of notes.

The fix queries tags directly through community_tags, avoiding both the redundant Node.find and the filtered association, while being more efficient by using pluck(:name) instead of loading full Tag objects.

Test plan

• Existing test test/unit/node_test.rb line 291 validates output: 'tag-test tag-awesome tag-spectrometer tag-activity-spectrometer tag-sub-tag'
• Verify note listing pages (/notes, /dashboard) render tag CSS classes correctly

Closes #11853

[aopv]

The original check logs expired; the surviving annotations show a GitHub cache outage and the upstream workflow using deprecated actions/upload-artifact v2. Since contributors cannot rerun this repository workflow directly, I pushed an empty retry commit to obtain fresh unit/integration results without mixing workflow changes into this PR.

[aopv]

Fresh run results confirm the PR code is not causing the red status: unit tests completed with 323 tests / 915 assertions / 0 failures / 0 errors, then failed only because the legacy Codecov uploader hit its unauthenticated rate limit. Functional tests failed in GitHub cache service; both system jobs are blocked by upstream actions/upload-artifact@v2; integration has 78 broad pre-existing argument-count errors across login/signup/moderation tests plus the same Codecov rate limit. No workflow-only changes were mixed into this model PR.