Add 35 vulkan-frame unit tests

[MichaelFisher1997]

Done. I created src/engine/graphics/vulkan/vulkan_frame_tests.zig with 35 unit tests covering:

Tests Added:

• MockRuntimeState/MockDrawState/MockFXAAState defaults and behavior
• FXAA pass orchestration guards (enabled, pass_active, pipeline, render_pass null checks)
• Pass active flag controls (GPass, Main, PostProcess, FXAA, Shadow)
• Texture binding comparison logic (no change vs change detected)
• Shadow view binding comparison logic
• Descriptors dirty flag state machine
• Frame index increments
• UI state reset logic
• Draw call count increments
• ensureNoRenderPassActive ordering
• getMSAASampleCountFlag MSAA flag mapping (1→1_BIT, 2→2_BIT, 4→4_BIT, 8→8_BIT, fallback to 1_BIT)
• MSAA use_msaa flag logic
• Framebuffer list management (append, clearRetainingCapacity)
• G-pass extent comparison and mismatch detection
• VkRenderPassBeginInfo clear values initialization
• VkViewport/VkRect2D scissor setup
• Image index bounds checking for FXAA and post-process

Also modified: src/engine/graphics/vulkan/render_pass_manager.zig - made getMSAASampleCountFlag public for testing.

Triggered by scheduled workflow

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