FN-6185: replace dashboard rgba fallbacks with color-mix

Convert remaining dashboard component rgba() fallbacks to color-mix() and extend the audit to cover the touched stylesheets.

- replace rgba() fallback colors with color-mix() in language selector, pull request, workflow, and settings component CSS
- expand the dashboard color tokenization audit to include the newly cleaned component stylesheets
- make the audit resolve settings component CSS from nested paths so SettingsFieldRow coverage works

Files changed:
 .../dashboard-component-color-tokenization.test.ts | 31 ++++++++++++++++------
 .../dashboard/app/components/LanguageSelector.css  |  2 +-
 .../dashboard/app/components/PullRequestView.css   | 20 +++++++-------
 .../app/components/WorkflowFieldsPanel.css         |  2 +-
 .../app/components/WorkflowNodeEditor.css          |  4 +--
 .../app/components/WorkflowSettingsPanel.css       |  2 +-
 .../app/components/settings/SettingsFieldRow.css   |  2 +-
 7 files changed, 39 insertions(+), 24 deletions(-)

Fusion-Task-Id: FN-6185

Fusion-Task-Lineage: b1938669-5ebb-4569-864b-bd64543ec843

packages/dashboard/app/components/WorkflowNodeEditor.css

@@ -42,7 +42,7 @@
   justify-content: space-between;
   gap: var(--space-sm);
   padding: var(--space-sm) var(--space-md);
-  background: var(--accent-subtle, rgba(59, 130, 246, 0.12));
+  background: var(--accent-subtle, color-mix(in srgb, #3b82f6 12%, transparent));
   border-bottom: 1px solid var(--border);
   color: var(--text);
   font-size: 0.85rem;
@@ -484,7 +484,7 @@
 
 .wf-templates-badge {
   padding: 0 var(--space-xs);
-  background: var(--accent-subtle, rgba(59, 130, 246, 0.12));
+  background: var(--accent-subtle, color-mix(in srgb, #3b82f6 12%, transparent));
   border-radius: var(--radius-sm);
   color: var(--text-muted);
   font-size: 0.7rem;