[qrrk]

Closes #218.

Changes

• Export Presets: Added data/*.json to include_filter in export_presets.cfg for both Linux and Windows presets.
• Default Settings: Extracted default launcher settings into res://data/default_settings.json and updated settings_manager.gd.
• PR Endpoints: Extracted changelog PR URLs into res://data/pr_endpoints.json and updated ChangelogDialod.gd.
• Modpacks: Extracted Kenan modpack definitions into res://data/modpacks.json and updated ModManager.gd.
• Soundpacks: Extracted soundpack configurations into res://data/soundpacks.json, refactored SoundpackManager.gd and SoundpacksUI.gd.
• Releases: Extracted release URLs and platform asset filters into res://data/release_sources.json and historical stable releases into res://data/stable_releases.json, removing ~380 lines of hardcoded data from ReleaseManager.gd.
• ZIP Extraction Optimization: Pre-creates directory hierarchies upfront and dispatches extraction across a worker thread pool (clampi(OS.get_processor_count(), 2, 16)), speeding up extraction of game archives by ~4.5x with zero external dependencies.