Pin graphics demo inputs and support explicit window mutation

[antono3]

Changes

• Pin released Vulkan and fixed ImGui/GLFW/compiler revisions in Linux and Windows builds.
• Pass the mutable Vulkan window explicitly for the V3-compatible ImGui bridge.
• Add a required pinned V3 frontend lane and keep current V/dependency master builds advisory.
• Pin workflow actions.

Verification

• Released V GCC demo compiled with both docking and standard bindings; both variants were visually exercised under Xvfb.
• Local pinned V3 frontend checks passed for both variants.
• PR CI covers Linux, Windows, and pinned V3.

The ImGui revision is supplied by antono2/imgui#32.