Document Vulkan Video design and simplify player layout

[antono3]

Summary

• Add a six-chapter learning guide that traces MP4 input through GPU selection, decode, synchronization, and presentation, with direct code and test links.
• Make the player one application package and split the former large player file into parser, session, decode, and presentation files.
• Update source-layout and build documentation.
• Build the Windows player with a console so documented commands such as --help and --list-gpus show diagnostics; check help output in Windows CI.

Verification

• V 0.5.2 with the release-pinned dependencies: v -cc gcc test . (3/3 test files passed) and executable build.
• Ubuntu/X11, NVIDIA GTX 1060: H.264 High Profile B-frame playback completed a display-order loop; window close and two resize cycles exited cleanly.
• --list-gpus reported the GTX 1060 compatible in coincident mode and rejected forced distinct mode as unsupported.
• All 73 guide source links and local heading links resolved after the final source edits.
• Windows 10, V 0.5.2/MSVC, antono2/vulkan at 6b182c9: package build and archive verification passed; player tests passed (3/3), and Vulkan ergonomic tests passed (5/5).
• The packaged Windows run.bat --list-gpus reports the GeForce GTX 765M as missing the three required Vulkan Video decode extensions. --help prints usage text.

Windows scope

Playback on a Windows machine with Vulkan Video-capable hardware remains a separate validation step.