Preserve CUE track metadata at launch

[Alexbeav]

Selecting a same-stem CUE currently replaces it with the BIN before mounting, so the runtime loses the CUE track layout. Use the existing resolve_disc_path(path).mount result at the launch adapter. Raw-only images, CHD and the resolver's unusable-CUE fallback retain their existing behavior.

The source-owned regression extracts the actual adapter and compiles it with the production resolver and parser. The unchanged adapter loses track metadata in four of eight synthetic cases; the corrected adapter passes all eight, including 12-track mixed media and eight-track audio-only media through both CUE and BIN entry points. It checks track numbers, types and starts.

Run python runtime/tests/test_launch_disc_path.py --help for the configured-compiler entry point. CTest registers the regression for GNU/Clang C++ builds.

Validation and limits

• Exact base: 8d56cf659fd84367c3f778e17851674ac7896371; review head: 7c11d57ea12812aa01587dcb5c313093ed1123d5.
• Native Windows GCC 16 runtime builds and passes 69/69 enabled runtime tests; two additional tests are disabled in the source configuration. The build has UI, setup wizard, debug tools, netplay, rewind and Vulkan disabled.
• Owned Wipeout XL (USA), canonical 12-track CUE with owned SCPH1001: verification, current-source generation, native build and an isolated 50-second startup pass; normal SDL window close at frame 3092, process exit 0. Executable SHA-256 49f53d0ef9bbf63a3a03f064534901434bf93bf601d8b4de811768ea84eac630. This is bounded startup and normal shutdown, not gameplay completion or listening acceptance. Audio used SDL dummy output. No native Linux/macOS game route is claimed.
• The unchanged current recompiler builds and has 58/61 enabled tests passing, with three pre-existing baseline failures (dirty_text_continuation_guards, aot_overlay_discovery, release_zip) and three disabled tests. This branch does not change that recompiler source. Those baseline failures are not reported as passes.
• Diff audit: general source repair, synthetic tests and documentation only; no retail disc/BIOS, generated game code, player data or private tooling.

Scope and fork review

Fork review #25 inspected this exact head against immutable review-base/mstan-8d56cf659fd8. Cubic reported no issues on the exact head (review IDs: 5132910678, 5132913804); no unresolved findings remain. The public PR branch points to the same commit. Upstream master was fetched again and remains the recorded base. This contribution contains 1 commit and 4 changed files.

• docs/LAUNCH_DISC_PATH.md: behavior and verification documentation.
• runtime/CMakeLists.txt: source-owned regression and test registration.
• runtime/src/main.cpp: bounded correction.
• runtime/tests/test_launch_disc_path.py: source-owned regression and test registration.

Developed with AI assistance; validated as described (test evidence in PR body). AI writes the code and the PR, but I always test before I send something up. Happy to iterate on this process with your feedback.