fix: Android initialization bug and iOS 14 availability annotations (#647)

* fix: Android initialization bug and iOS 14 availability annotations

- Fix Android PlatformException on first run after initialize (fixes #645)
  - Update currentDispatcherHandle when initialize() is called
  - Add validation for callback handle
- Add iOS 14.0 availability annotation to LoggingDebugHandler (fixes #641)
  - Prevents build errors when os.Logger is used
- Update documentation with iOS 14.0 minimum deployment target requirement (fixes #639)

Co-Authored-By: Claude <noreply@anthropic.com>

* docs: add version management guidelines for melos workflow

* chore: regenerate pigeon files after pub upgrade

* fix: remove invalid handle validation that was rejecting valid callback handles

The handle validation was too strict and incorrectly rejected valid callback
handles (including 0) which caused all initialize calls to fail in integration tests

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Co-authored-by: Claude <noreply@anthropic.com>