Implement FSR 2.2 temporal upscaling

Full FSR 2.2 pipeline with depth-based motion vector reprojection,
temporal accumulation with YCoCg neighborhood clamping, and RCAS
contrast-adaptive sharpening.

Architecture (designed for FSR 3.x frame generation readiness):
- Camera: Halton(2,3) sub-pixel jitter with unjittered projection
  stored separately for motion vector computation
- Motion vectors: compute shader reconstructs world position from
  depth + inverse VP, reprojects with previous frame's VP
- Temporal accumulation: compute shader blends 5-10% current frame
  with 90-95% clamped history, adaptive blend for disocclusion
- History: ping-pong R16G16B16A16 buffers at display resolution
- Sharpening: RCAS fragment pass with contrast-adaptive weights

Integration:
- FSR2 replaces both FSR1 and MSAA when enabled
- Scene renders to internal resolution framebuffer (no MSAA)
- Compute passes run between scene and swapchain render passes
- Camera cut detection resets history on teleport
- Quality presets shared with FSR1 (0.50-0.77 scale factors)
- UI: "Upscaling" combo with Off/FSR 1.0/FSR 2.2 options

assets/shaders/fsr2_sharpen.frag.glsl

@@ -0,0 +1,46 @@
+#version 450
+
+layout(location = 0) in vec2 TexCoord;
+layout(location = 0) out vec4 FragColor;
+
+layout(set = 0, binding = 0) uniform sampler2D inputImage;
+
+layout(push_constant) uniform PushConstants {
+    vec4 params;  // x = 1/width, y = 1/height, z = sharpness (0-2), w = unused
+} pc;
+
+void main() {
+    vec2 texelSize = pc.params.xy;
+    float sharpness = pc.params.z;
+
+    // RCAS: Robust Contrast-Adaptive Sharpening
+    // 5-tap cross pattern
+    vec3 center = texture(inputImage, TexCoord).rgb;
+    vec3 north  = texture(inputImage, TexCoord + vec2(0.0, -texelSize.y)).rgb;
+    vec3 south  = texture(inputImage, TexCoord + vec2(0.0,  texelSize.y)).rgb;
+    vec3 west   = texture(inputImage, TexCoord + vec2(-texelSize.x, 0.0)).rgb;
+    vec3 east   = texture(inputImage, TexCoord + vec2( texelSize.x, 0.0)).rgb;
+
+    // Compute local contrast (min/max of neighborhood)
+    vec3 minRGB = min(center, min(min(north, south), min(west, east)));
+    vec3 maxRGB = max(center, max(max(north, south), max(west, east)));
+
+    // Adaptive sharpening weight based on local contrast
+    // High contrast = less sharpening (prevent ringing)
+    vec3 range = maxRGB - minRGB;
+    vec3 rcpRange = 1.0 / (range + 0.001);
+
+    // Sharpening amount: inversely proportional to contrast
+    float luma = dot(center, vec3(0.299, 0.587, 0.114));
+    float lumaRange = max(range.r, max(range.g, range.b));
+    float w = clamp(1.0 - lumaRange * 2.0, 0.0, 1.0) * sharpness * 0.25;
+
+    // Apply sharpening via unsharp mask
+    vec3 avg = (north + south + west + east) * 0.25;
+    vec3 sharpened = center + (center - avg) * w;
+
+    // Clamp to prevent ringing artifacts
+    sharpened = clamp(sharpened, minRGB, maxRGB);
+
+    FragColor = vec4(sharpened, 1.0);
+}