Added skill for debugging with React Native Devtools

plugins/expo-app-design/skills/debugging/SKILL.md

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+---
+name: debugging
+description: Guide for debugging Expo and React Native apps. Covers React Native DevTools, breakpoints, console, network inspection, error handling, and profiling.
+version: 1.0.0
+license: MIT
+---
+
+# Debugging Expo Apps
+
+## Quick Start
+
+1. Start the dev server: `npx expo start`
+2. Press **j** to open **React Native DevTools**
+3. Use the **Sources** tab to set breakpoints and step through code
+
+React Native DevTools requires **Hermes** (default since SDK 49) and works with Expo Go and dev clients.
+
+## React Native DevTools
+
+Open by pressing **j** in the Expo CLI terminal.
+
+### Sources — Breakpoints & Stepping
+
+- Click a **line number** in the Sources tab to add a breakpoint
+- Or add `debugger;` statements directly in your code
+- When paused, inspect variables and functions in scope
+- Step through code with standard controls (step over, step into, step out, continue)
+- Use the Console while paused to evaluate expressions in the current scope
+
+```tsx
+function handlePress() {
+  debugger; // App pauses here when DevTools is connected
+  const result = computeValue();
+  console.log(result);
+}
+```
+
+### Pause on Exceptions
+
+- Enable **Pause on exceptions** in the right panel of the Sources tab
+- Toggle **Pause on caught exceptions** to catch errors handled by try/catch or error boundaries
+
+### Console
+
+- Execute JavaScript as if it were part of your app
+- When paused at a breakpoint, runs in that breakpoint's scope
+
+### Other Tabs
+
+- **Network** (Expo only): inspect `fetch` requests and responses
+- **Memory**: heap snapshots to diagnose memory leaks
+- **Components**: inspect the React component tree, props, and styles
+- **Profiler**: record and analyze JS performance (debug builds only)
+
+## Developer Menu
+
+Open with **m** in the Expo CLI terminal (or **Ctrl + Cmd + Z** / **Cmd + D** on iOS Simulator, **Cmd + M** on Android Emulator). Provides performance monitor, element inspector, Fast Refresh toggle, and reload.
+
+## Errors and Warnings
+
+- **Redbox**: fatal error — unhandled exceptions or `console.error()`
+- **Yellowbox**: warning — `console.warn()`
+- Always read the **file name** and **line number** in the stack trace first
+
+## Debugging Strategies
+
+1. **Search first**: error message on Google, Stack Overflow, [Expo forums](https://chat.expo.dev/)
+2. **Isolate**: revert to working state, apply changes piece by piece until it breaks
+3. **Simplify**: remove libraries (state management, navigation) to narrow down the source
+4. **Use breakpoints**: prefer over `console.log` — inspect the full scope
+5. **Minimal repro**: extract failing code into a blank `npx create-expo-app` project
+
+## Production Debugging
+
+- Test production mode locally: `npx expo start --no-dev --minify`
+- Use [Sentry](https://docs.expo.dev/guides/using-sentry) or [BugSnag](https://docs.expo.dev/guides/using-bugsnag) for crash reporting
+- For native crashes, check logs with `adb logcat` (Android) or Xcode Console (iOS)