test(mobile): add comprehensive test infrastructure and initial test suite

Implemented complete testing setup with Jest and React Native Testing Library:

## Test Infrastructure

**Files Created:**
1. `mobile/jest.config.js` - Jest configuration with:
   - jest-expo preset for React Native/Expo
   - Module name mapping for @pezkuwi/* (shared library)
   - Transform ignore patterns for node_modules
   - Coverage thresholds: 70% statements, 60% branches, 70% functions/lines
   - Test match pattern: **/__tests__/**/*.test.(ts|tsx|js)

2. `mobile/jest.setup.js` - Test setup with mocks:
   - expo-linear-gradient mock
   - expo-secure-store mock (async storage operations)
   - expo-local-authentication mock (biometric auth)
   - @react-native-async-storage/async-storage mock
   - @polkadot/api mock (blockchain API)
   - Supabase mock (auth and database)
   - Console warning/error suppression in tests

3. `mobile/package.json` - Added test scripts:
   - `npm test` - Run all tests
   - `npm run test:watch` - Watch mode for development
   - `npm run test:coverage` - Generate coverage report

---

## Test Suites

### 1. Context Tests

**File:** `mobile/src/contexts/__tests__/AuthContext.test.tsx`

Tests for AuthContext (7 test cases):
- ✅ Provides auth context with initial state
- ✅ Signs in with email/password
- ✅ Handles sign in errors correctly
- ✅ Signs up new user with profile creation
- ✅ Signs out user
- ✅ Checks admin status
- ✅ Proper async handling and state updates

**Coverage Areas:**
- Context initialization
- Sign in/sign up flows
- Error handling
- Supabase integration
- State management

---

### 2. Component Tests

**File:** `mobile/src/components/__tests__/ErrorBoundary.test.tsx`

Tests for ErrorBoundary (5 test cases):
- ✅ Renders children when no error occurs
- ✅ Renders error UI when child throws error
- ✅ Displays "Try Again" button on error
- ✅ Renders custom fallback if provided
- ✅ Calls onError callback when error occurs

**Coverage Areas:**
- Error catching mechanism
- Fallback UI rendering
- Custom error handlers
- Component recovery

---

### 3. Integration Tests

**File:** `mobile/__tests__/App.test.tsx`

Integration tests for App component (3 test cases):
- ✅ Renders App component successfully
- ✅ Shows loading indicator during i18n initialization
- ✅ Wraps app in ErrorBoundary (provider hierarchy)

**Coverage Areas:**
- App initialization
- Provider hierarchy validation
- Loading states
- Error boundary integration

---

## Test Statistics

**Total Test Files:** 3
**Total Test Cases:** 15
**Coverage Targets:** 70% (enforced by Jest config)

### Test Distribution:
- Context Tests: 7 cases (AuthContext)
- Component Tests: 5 cases (ErrorBoundary)
- Integration Tests: 3 cases (App)

---

## Mocked Dependencies

All external dependencies properly mocked for reliable testing:
- ✅ Expo modules (LinearGradient, SecureStore, LocalAuth)
- ✅ AsyncStorage
- ✅ Polkadot.js API
- ✅ Supabase client
- ✅ React Native components
- ✅ i18n initialization

---

## Running Tests

```bash
# Run all tests
npm test

# Watch mode (for development)
npm run test:watch

# Coverage report
npm run test:coverage
```

---

## Future Test Additions

Recommended areas for additional test coverage:
- [ ] PolkadotContext tests (wallet connection, blockchain queries)
- [ ] Screen component tests (SignIn, SignUp, Governance, etc.)
- [ ] Blockchain transaction tests (mocked pallet calls)
- [ ] Navigation tests
- [ ] E2E tests with Detox

---

## Notes

- All tests use React Native Testing Library best practices
- Async operations properly handled with waitFor()
- Mocks configured for deterministic test results
- Coverage thresholds enforced at 70%
- Tests run in isolation with proper cleanup

mobile/src/components/__tests__/ErrorBoundary.test.tsx

@@ -0,0 +1,81 @@
+import React from 'react';
+import { render, screen } from '@testing-library/react-native';
+import { Text } from 'react-native';
+import { ErrorBoundary } from '../ErrorBoundary';
+
+// Component that throws error for testing
+const ThrowError = () => {
+  throw new Error('Test error');
+  return null;
+};
+
+// Normal component for success case
+const SuccessComponent = () => <Text>Success!</Text>;
+
+describe('ErrorBoundary', () => {
+  // Suppress error console logs during tests
+  const originalError = console.error;
+  beforeAll(() => {
+    console.error = jest.fn();
+  });
+
+  afterAll(() => {
+    console.error = originalError;
+  });
+
+  it('should render children when no error occurs', () => {
+    render(
+      <ErrorBoundary>
+        <SuccessComponent />
+      </ErrorBoundary>
+    );
+
+    expect(screen.getByText('Success!')).toBeTruthy();
+  });
+
+  it('should render error UI when child throws error', () => {
+    render(
+      <ErrorBoundary>
+        <ThrowError />
+      </ErrorBoundary>
+    );
+
+    expect(screen.getByText('Something Went Wrong')).toBeTruthy();
+    expect(screen.getByText(/An unexpected error occurred/)).toBeTruthy();
+  });
+
+  it('should display try again button on error', () => {
+    render(
+      <ErrorBoundary>
+        <ThrowError />
+      </ErrorBoundary>
+    );
+
+    expect(screen.getByText('Try Again')).toBeTruthy();
+  });
+
+  it('should render custom fallback if provided', () => {
+    const CustomFallback = () => <Text>Custom Error UI</Text>;
+
+    render(
+      <ErrorBoundary fallback={<CustomFallback />}>
+        <ThrowError />
+      </ErrorBoundary>
+    );
+
+    expect(screen.getByText('Custom Error UI')).toBeTruthy();
+  });
+
+  it('should call onError callback when error occurs', () => {
+    const onError = jest.fn();
+
+    render(
+      <ErrorBoundary onError={onError}>
+        <ThrowError />
+      </ErrorBoundary>
+    );
+
+    expect(onError).toHaveBeenCalled();
+    expect(onError.mock.calls[0][0].message).toBe('Test error');
+  });
+});