Add Expo playground for end-to-end agent-cdp verification

[V3RON]

Summary

• add an Expo SDK 55 playground app to the workspace as a live React Native target for agent-cdp
• replace the starter UI with a minimal button-only harness that triggers retained-memory, transient-allocation, console, and profiling scenarios for end-to-end inspection
• add repository guidance for validating runtime-inspection changes through the playground with agent-device and native dev-client flows

Testing

• pnpm --dir playground lint
• pnpm --dir playground exec tsc --noEmit
• agent-device snapshot -i --platform ios --session default
• pnpm run agent-cdp -- console list --limit 10
• pnpm run agent-cdp -- js-memory sample --label verify-now --gc
• pnpm run agent-cdp -- js-profile summary --session js_1