Fix WCAG AA color contrast violations across all pages

Replace incorrect perceived-brightness formula in Stats progress bars
with proper WCAG relative luminance calculation, and convert type bar
colors to hex values for reliable contrast detection. Add light: variant
classes to status badges, yellow/purple text, and admin nav links across
17 files. Darken light-mode status-active token and text-tertiary/muted
tokens. Add aria-labels to admin filter selects and flex-wrap for mobile
overflow on AdminEvolutions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/e2e/accessibility.spec.ts

@@ -44,12 +44,16 @@ for (const theme of themes) {
           id: v.id,
           impact: v.impact,
           description: v.description,
-          nodes: v.nodes.length,
+          nodes: v.nodes.map((n) => ({
+            html: n.html,
+            target: n.target,
+            failureSummary: n.failureSummary,
+          })),
         }))
 
         expect(
           violations,
-          `${name} (${theme}): ${violations.length} accessibility violations found:\n${JSON.stringify(violations, null, 2)}`,
+          `${name} (${theme}): ${violations.length} violation(s):\n${JSON.stringify(violations, null, 2)}`,
         ).toHaveLength(0)
       })
     }