style: fix badge centering over flags, plain theme toggle icon

- badgeRow now uses same gap (10px) as matchRow for exact alignment
- Theme toggle: removed button box, plain icon like admin gear
- Both icons use text-secondary color, consistent style

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

frontend/src/App.module.css

@@ -74,21 +74,18 @@
 }
 
 .themeToggle {
-  background: var(--surface-high);
-  border: 1px solid var(--border-subtle);
-  border-radius: var(--radius-sm);
-  width: 34px;
-  height: 34px;
+  background: none;
+  border: none;
   display: flex;
   align-items: center;
   justify-content: center;
-  font-size: 16px;
+  padding: 4px;
   cursor: pointer;
-  transition: background 0.15s, transform 0.1s;
+  transition: color 0.2s;
   flex-shrink: 0;
-  color: var(--gold);
+  color: var(--text-secondary);
 }
-.themeToggle:hover { background: var(--primary-dim); }
+.themeToggle:hover { color: var(--text-primary); }
 .themeToggle:active { transform: scale(0.92); }
 
 .main {