Version 0.5.0 - Major code refactoring

Broke down monolithic editor.js into focused, maintainable modules:
- vtt-utils.js: VTT/subtitle utility functions
- timeline-renderer.js: Quality timeline rendering
- subtitle-list-renderer.js: Subtitle list rendering
- video-controls.js: Video playback controls and setup
- editor-actions.js: API action functions
- editor-insert-modal.js: Insert segment modal
- editor-manual-edit-modal.js: Manual VTT edit modal
- editor-reset-modal.js: Reset segment modal
- editor-gitlab-push-modal.js: GitLab push modal

Reduced editor.js from 1614 to ~715 lines (56% reduction)
Improved separation of concerns and code maintainability