Add dark theme + auto accent color overrides

Use off-white backgrounds with dark text for active/selected elements
when using dark theme with 'auto' accent color:
- Tab buttons (active state)
- Sidebar nav items (active state)
- Primary buttons
- Toggle switches
- Badges, checkboxes, input focus states
- Theme settings cards and options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/styles/theme/index.css

@@ -102,4 +102,26 @@ button:focus-visible {
 
 ::-webkit-scrollbar-thumb:hover {
   background: var(--color-border-hover);
+}
+
+/* ==========  DARK THEME + AUTO ACCENT OVERRIDES ========== */
+
+/* Links */
+[data-theme='dark'][data-accent='auto'] a {
+  color: #e5e7eb;
+}
+
+[data-theme='dark'][data-accent='auto'] a:hover {
+  color: #f3f4f6;
+}
+
+/* Button focus outline */
+[data-theme='dark'][data-accent='auto'] button:focus,
+[data-theme='dark'][data-accent='auto'] button:focus-visible {
+  outline-color: #e5e7eb;
+}
+
+/* Loading state */
+[data-theme='dark'][data-accent='auto'] .loading {
+  color: #e5e7eb;
 }