refactor(store): Extract utility functions into store/utils/

Move pure utility functions from app-store.ts and type files into
dedicated utils modules for better separation of concerns:

- theme-utils.ts: Theme and font storage utilities
- shortcut-utils.ts: Keyboard shortcut parsing/formatting
- usage-utils.ts: Usage limit checking

All utilities are re-exported from store/utils/index.ts and
app-store.ts maintains backward compatibility for existing imports.

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

apps/ui/src/store/utils/usage-utils.ts

@@ -0,0 +1,34 @@
+import type { ClaudeUsage } from '../types/usage-types';
+
+/**
+ * Check if Claude usage is at its limit (any of: session >= 100%, weekly >= 100%, OR cost >= limit)
+ * Returns true if any limit is reached, meaning auto mode should pause feature pickup.
+ */
+export function isClaudeUsageAtLimit(claudeUsage: ClaudeUsage | null): boolean {
+  if (!claudeUsage) {
+    // No usage data available - don't block
+    return false;
+  }
+
+  // Check session limit (5-hour window)
+  if (claudeUsage.sessionPercentage >= 100) {
+    return true;
+  }
+
+  // Check weekly limit
+  if (claudeUsage.weeklyPercentage >= 100) {
+    return true;
+  }
+
+  // Check cost limit (if configured)
+  if (
+    claudeUsage.costLimit !== null &&
+    claudeUsage.costLimit > 0 &&
+    claudeUsage.costUsed !== null &&
+    claudeUsage.costUsed >= claudeUsage.costLimit
+  ) {
+    return true;
+  }
+
+  return false;
+}