Add offline transcript auto edit cleanup

[karansinghgit]

Summary

• add an optional offline auto-edit pass that removes common filler words after transcription
• support custom phrase replacement rules from Settings, including blank replacements for deletions
• add a Transcript Cleanup settings section with toggle, examples, and inline help

Validation

• xcodebuild build -scheme speaktype -destination 'platform=macOS'

Closes #53