feat(vk): Vk.* - Vulkan 1.0-1.4 generated from the registry, loaded at run time

ludic-dev vkgen reads vk.xml into runtime/native/vk_api.ludic (constants, every struct's
<Struct>_sizeof and <Struct>_<field> offsets, one extern per command) and vk_thunks.ll.
Every size and offset was compiled against the SDK's C headers; `ludic-dev test` checks the
tracked files against the registry wherever the Vulkan SDK is installed.

vk_win.ll (vulkan-1.dll) and vk_mac.ll (libvulkan.1.dylib, MoltenVK) open the loader at run
time, so a program built with Vk.* starts on a machine without Vulkan. ludicc and ludic
build link both for any program that uses Vk.*. The seeds are regenerated for the new
compiler.

vk_probe reports what a machine's Vulkan can do; vk_compute dispatches a Slang compute
shader and reads the picture back, clean under the validation layer on an RTX 3070 Ti and
on an M4 Pro through MoltenVK.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

runtime/native/vk_win.ll

@@ -0,0 +1,61 @@
+; ============================================================================
+; vk_win.ll — the Vulkan loader, for Windows, written in LLVM IR.
+;
+; vulkan-1.dll ships with every GPU driver on Windows 10 and 11, but it is not
+; guaranteed, so it is opened AT RUN TIME and never linked: a program that asks for
+; Vulkan on a machine without it gets 0 from vk_open and falls back to OpenGL
+; rather than failing to start.
+;
+;   lvk_open() -> 1 | 0      open the loader and bind every command (vk_thunks.ll)
+;   lvk_sym(name) -> ptr     one entry point by name, null when the loader lacks it
+;   lvk_has(name) -> 1 | 0   whether a command is there (an extension's, say)
+;
+; The commands themselves, their struct layouts and constants are generated from
+; the Vulkan registry by `ludic-dev vkgen` into vk_api.ludic and vk_thunks.ll.
+; ============================================================================
+
+declare ptr @LoadLibraryA(ptr)
+declare ptr @GetProcAddress(ptr, ptr)
+declare i32 @lvk_bind()
+
+@.lvk_dll = private unnamed_addr constant [13 x i8] c"vulkan-1.dll\00"
+@lvk_lib  = internal global ptr null
+
+define i32 @lvk_open() {
+entry:
+  %have = load ptr, ptr @lvk_lib
+  %open = icmp ne ptr %have, null
+  br i1 %open, label %ok, label %load
+load:
+  %lib = call ptr @LoadLibraryA(ptr @.lvk_dll)
+  %none = icmp eq ptr %lib, null
+  br i1 %none, label %fail, label %bind
+bind:
+  store ptr %lib, ptr @lvk_lib
+  %n = call i32 @lvk_bind()
+  br label %ok
+ok:
+  ret i32 1
+fail:
+  ret i32 0
+}
+
+define ptr @lvk_sym(ptr %name) {
+entry:
+  %lib = load ptr, ptr @lvk_lib
+  %none = icmp eq ptr %lib, null
+  br i1 %none, label %no, label %look
+look:
+  %p = call ptr @GetProcAddress(ptr %lib, ptr %name)
+  ret ptr %p
+no:
+  ret ptr null
+}
+
+define i32 @lvk_has(ptr %name) {
+entry:
+  %p = call ptr @lvk_sym(ptr %name)
+  %there = icmp ne ptr %p, null
+  %r = zext i1 %there to i32
+  ret i32 %r
+}