Keep the runtime's shaders in the repository as source only, and compile them when the game is built.

The fifteen headers of SPIR-V words under runtime/ are no longer tracked. tools/build_shaders.py builds all of them:
the GLSL with glslc, the SPIR-V assembly with spirv-as, and the two shaders assembled in Python from their scripts.
build_game.py builds the missing and the stale ones before it compiles the runtime, and the build kit, the launcher
release and the AppImage build them before they copy runtime/, so a player's PC still needs no shader compiler.
git ignores the headers and check_content.py refuses a compiled shader in a commit. The headers built this way are
byte for byte the ones removed here. vk_mvobj_fs.h is now mvobj_fs_spv.h, named like the others.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -4,6 +4,8 @@
 
 Nothing that came out of the game goes into the repository: no game files, keys, extracted data, recompiled C, compiled binaries, shaders, shader caches, fonts, audio or movies. Not in commits, not in issues, not in pull requests. Only information about the game goes in: addresses, hashes, patch code we wrote, shader and bind-state identifiers.
 
+Our own shaders go in as source only (`runtime/shaders/`, `tools/make_dlaa_mask.py`, `tools/make_mvobj_fs.py`); the build compiles them (`tools/build_shaders.py`), and the same checks refuse a compiled one.
+
 Two checks enforce this:
 
 - CI runs `tools/check_content.py` on every push and pull request.