Fix: Critical crash in filter menu and Fastlane UI import issue (#51)

* fix: add Fastlane UI import to changelog_helper

- Changed from Fastlane.const_defined?(:UI) to defined?(UI)
- Fixes NameError: uninitialized constant ChangelogHelper::UI

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

* fix: prevent crash when filter menu content is empty

- Changed OR (||) to AND (&&) in FeedInfo.isValid()
- Prevents index out of range crash when items array is empty
- Fixes crash reported in TestFlight feedback

Crash details:
- Swift runtime failure: Index out of range
- Location: FeedInfo.isValid() accessing items[0] on empty array
- Trigger: Filter menu with no corresponding content

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

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

Author: graycreate