fix(example): prevent duplicate Metro peer deps

[markm39]

Summary

• force the example Metro config to resolve React Native runtime peer dependencies from example/node_modules
• block package-root peer dependency copies from the watched monorepo package root
• keep @mathnotes/mobile-ink mapped to the local package source for example development

Why

Running the example from Xcode UI could load both example/node_modules and ../node_modules copies of React Native / gesture-handler / reanimated / worklets. That duplicated React Native dev environment setup and crashed with:

TypeError: property is not writable while defining global.__FUSEBOX_REACT_DEVTOOLS_DISPATCHER__.

Verification

• node -c example/metro.config.js
• npm run typecheck
• npm run test:example:typecheck
• npm run test:example:export:ios
• Generated a dev iOS bundle from npx expo start --dev-client --clear --port 8101 and confirmed it contains no package-root copies matching ../node_modules/(react-native|react-native-gesture-handler|react-native-reanimated|react-native-worklets)

Security / dependency note

• Simplify review: no findings.
• Security review: no findings in the changed config.
• npm audit --omit=dev --audit-level=moderate still reports a pre-existing Expo/PostCSS advisory in the example dependency graph. The suggested automated fix is breaking and unrelated to this Metro resolver change, so this PR does not alter dependencies.