chore: bump iOS/watchOS deployment targets for latest SDK compatibility

[kinyoklion]

Summary

Bumps minimum deployment targets so the example app can resolve and use the latest LaunchDarkly iOS SDK (10.0+/11.x).

The SDK's 10.0.0 release dropped support for iOS 12 and watchOS 4.0. Since the Podfile specifies >= 9.6, CocoaPods would silently pin to the latest 9.x when the platform minimum is too low for 10.0+. This update raises the floors to match the SDK's current podspec requirements:

• iOS: 12.0 → 13.0 (Podfile + all IPHONEOS_DEPLOYMENT_TARGET entries in the Xcode project, including the project-level 10.0 entries)
• watchOS: 4.0 → 6.0 (Podfile + all WATCHOS_DEPLOYMENT_TARGET entries)

Related PRs in sibling repos: hello-ios-swift and hello-tvos.

Review & Testing Checklist for Human

• Open the project in Xcode after running pod install and verify it resolves to an SDK version ≥ 10.0 (ideally 11.x)
• Build and run on an iOS 13+ simulator to confirm the Objective-C code and watchOS extension still compile cleanly against the latest SDK
• Verify the watchOS extension target also builds (deployment target 6.0 matches the SDK podspec's watchos.deployment_target)

Notes

• The README does not mention specific platform version requirements, so no README changes were included.
• These changes were not build-tested — no Xcode environment was available. A local pod install + build is the recommended verification step.

Link to Devin session: https://app.devin.ai/sessions/79411e068f79496bbbb41d24c39cffd4
Requested by: @kinyoklion

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