fix(dashboard): improve kanban code contrast

[flyespresso]

Summary

• Force Kanban markdown inline code and fenced code blocks to use the active theme foreground color
• Clear inherited text shadows on code/pre blocks so theme-specific code styling cannot reduce contrast
• Add a regression test that checks the Kanban dashboard CSS keeps code contrast tied to foreground

Test Plan

• python -m pytest tests/plugins/test_kanban_dashboard_plugin.py -q -o 'addopts='

[teknium1]

Closed in favor of PR #20687 (commit 17687911, by @liuguangyong93).

Your PR had the broadest scope — patching `-event-payload`, `-run-meta`, `-md`, `-md-code`, `-md code`, and adding `text-shadow: none` across the kanban surface, plus a regression test. The merged fix takes a different route: one scoped `.hermes-kanban code` override that cascades to every `` element in the board (event-payload and run-meta both render as ``), beating the Nous DS global `code { background: var(--midground) }` rule on specificity.

Result is the same readable contrast with a 9-line diff instead of ~30 selector patches.

Thanks for the detailed diagnosis and the test — the test pattern (asserting CSS content against the bundle) is good and we'll likely lift it in a later cleanup pass.

#20687