Support V3 standard ImGui bindings and pin Vulkan release

[antono3]

Changes

• Apply Vulkan v2.0.0 pin and V3 generated-binding/bridge fixes to the standard ImGui branch.
• Expose GLFW C declarations to MSVC and update the Windows demo revision.
• Require stable Linux/Windows builds and pinned V3 frontend check; keep current V/dependency master advisory.
• Pin workflow actions and correct v.mod author metadata.

Verification

• Binding cleanup self-test and direct pinned V3 checks passed locally.
• Released V GCC demo compiled after the generated changes; standard UI was visually exercised under Xvfb.
• PR CI covers Linux, Windows, and pinned V3.

The full V3 C backend issue is described in #32.