Use installed game soundtracks instead of bundled music

[Maxaubert]

Removes bundled soundtrack albums from the installer and release pipeline. A fresh installation discovers music in the user's Steam libraries, reads Bonus Content audio in place and caches decoded MG2 opening themes and the MGS2 main theme locally. Selected music is ready before the menus appear. Personal music and saved choices remain supported.

The Bonus Content playlist combines available native classics with personal tracks, preserving distinct recordings from different games. Missing installations and optional songs are skipped safely. MGS1, MGS3, MGS4 and Peace Walker obtain their defaults from installed Bonus Content. Game opening edits can differ in length from album versions.

Matching personal format copies and installed titles share one music row, preferring lossless personal audio and retaining previous selection IDs as aliases. Source files remain untouched.

Music is now normalized per track using integrated, K-weighted gated loudness. This fixes large level differences between album copies and installed recordings. The reference is the installed MGS3 Snake Eater track at approximately -19.6 LUFS, with playback 10% above its previous level. Game music, previews and the Bonus playlist share the correction, with bounded amplification and sample-peak headroom. User volume, mute, fades and sound effects retain their behavior. Measurements are prepared before menus open and cached as small records; no converted soundtrack copies are created for normalization.

Version: 0.13.2. One music-free MetalGearLauncher-Setup-x64-0.13.2.exe replaces Full/Lite packaging. The pinned vgmstream decoder ships with codec libraries, license notices and source links. The installer remains unsigned.

Validation:

• Typecheck, lint and all 378 unit tests passed. CI passed on eb34b49.
• Ran the full 59-test Electron suite: 58 passed, with a keyboard-hints test sending input before the splash finished. Its readiness check was corrected; all four targeted startup, audible-normalization and keyboard tests then passed. No unresolved test failures.
• Independent review found no blocking issues.
• Real installed defaults from all six games and the personal MGS1 Introduction recording reach the same calculated output loudness, approximately -21.27 LUFS at the default volume. Independent FFmpeg measurements agree with the analyzer. Cached catalog verification took 332 ms after initial analysis.
• The packaged app played the user's FLAC Introduction with measured gain 0.4345 and volume 0.825; an audio analyser confirmed nonzero output. Eighteen personal MGS1 files produce nine rows, with all files preserved. A browser signal test verifies a threefold gain change rather than only checking that playback time advances.
• Steam trophies detect the local most-recent login. Fourteen account/parsing/cache tests passed, including account switching and cache isolation. Installer inspection found no personal account IDs or account caches.
• Clean local installation reports ProductVersion 0.13.2.0, decoder installed, zero bundled soundtrack files and no configuration or extraction cache. Personal music and sounds are preserved. The installation is left unopened for first-run testing.

Includes the approved monochrome Snake icon for the application, executable, shortcuts and installer. This branch contains the icon changes from PR #49 and now targets main directly, superseding that separate PR. Merge approved by Ove. Closes #50. Closes #48.