feat(kanban): add grab-to-pan board scrolling

[vampyren]

Summary

• Adds grab-to-pan horizontal scrolling to the Kanban dashboard board columns.
• Shows grab / grabbing cursor feedback while preserving card drag, add buttons, checkboxes, links, inputs, and other interactive controls.
• Keeps the native horizontal scrollbar usable as a fallback and clears the panning state on mouse release or window blur.

Test plan

• git diff --check -- plugins/kanban/dashboard/dist/index.js plugins/kanban/dashboard/dist/style.css
• node --check plugins/kanban/dashboard/dist/index.js
• scripts/run_tests.sh tests/plugins/test_kanban_dashboard_plugin.py
• Playwright smoke test against http://localhost:9119/kanban: verified cursor states, horizontal scroll movement, blur cleanup, and card mouse-down exclusion.

[vampyren]

Screencast_20260706_220359.webm
Short demo :)

[teknium1]

Merged via PR #60226 — your grab-to-pan change is now on main with your authorship preserved in git history (cherry-picked and rebase-merged).

The only issue with this PR was the commit metadata: it was authored as Rex <rex@local>, a local git identity not linked to your GitHub account, which failed our attribution CI check. The code itself was great — clean exclusion handling for cards/controls, proper listener cleanup, native scrollbar fallback. Nothing else needed changing.

For future PRs, set your git identity to your GitHub noreply address so commits link to your account:

git config --global user.name "vampyren"
git config --global user.email "4087127+vampyren@users.noreply.github.com"

Thanks for the contribution!

[vampyren]

Merged via PR #60226 — your grab-to-pan change is now on main with your authorship preserved in git history (cherry-picked and rebase-merged).

The only issue with this PR was the commit metadata: it was authored as Rex <rex@local>, a local git identity not linked to your GitHub account, which failed our attribution CI check. The code itself was great — clean exclusion handling for cards/controls, proper listener cleanup, native scrollbar fallback. Nothing else needed changing.

For future PRs, set your git identity to your GitHub noreply address so commits link to your account:

Thank you! Will fix the account. Just moved to a new pc and its still not properly setup.
Cheers