Deprecate CocoaPods support and remove from release pipeline

[ioannisj]

Description

CocoaPods trunk is moving to be read-only by the end of the year, December 2nd 2026.

After this date, no new podspecs or versions can be published to trunk. Existing versions will remain installable, but releases will effectively be frozen.

Although we have ~11 months, migration across customer codebases takes time. To avoid a last-minute transitions and reduce transitioning burden, we should proactively move away from CocoaPods and standardize Swift Package Manager

Proposed plan

• Announce deprecation of CocoaPods support in README and release notes.
• Remove CocoaPods publishing from the release pipeline.
• Remove the .podspec from the repository.
• Update documentation to only reference Swift Package Manager.
• Add a migration guide for existing CocoaPods users.

Hybrid SDKs / Plugins

Both posthog-flutter and posthog-react-native-session-replay currently rely on CocoaPods to pull in the native posthog-ios SDK:

• Flutter:
  • Still recommends using CocoaPods
  • SPM support is under development and still opt-in. Flutter falls back to CocoaPods for dependencies that don't support SPM yet.
• React Native:
  • Since React Native 0.75, there's been a solution to integrate SPM packages into React Native applications through the spm_dependency helper that allows libraries to consume SPM packages alongside CocoaPods.
  • React Native is actively moving toward SPM as the preferred iOS dependency manager, but this is still in development