fix: comprehensive a11y and contrast QA pass across workbench

Automated QA loop (6 parallel browser agents, 2 rounds) found and fixed
15 accessibility, contrast, and responsive issues across all 8 pages:

- WCAG contrast: light-mode warning (#854d0e), error (#b91c1c), toggle
  off-state (surface-400), connection badge (fg-muted)
- ARIA: mode selector group+pressed, tab pattern ids+labelledby, nav
  and aside labels, dialog focus-return, alert roles on banners
- Responsive: library header flex-wrap, search/button aria-labels
- Focus: NavLink visible ring, dialog close button ring

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.idea/GitLink.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="uk.co.ben_gibson.git.link.SettingsState">
+    <option name="host" value="72037fcc-cb9c-4c22-960a-ffe73fd5e229" />
+  </component>
+</project>

.idea/discord.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="DiscordProjectSettings">
+    <option name="show" value="ASK" />
+    <option name="description" value="" />
+  </component>
+</project>