fix: remove Y-flip counter-hacks in FSR shaders; invert mouse by default; FSR1 disables MSAA

FSR EASU and FSR2 sharpen fragment shaders had a manual Y-flip to undo
the now-removed postprocess.vert flip.  Strip those since the vertex
shader no longer flips, making all postprocess paths consistent.

Also flip the default mouse Y-axis to match user expectation (mouse
down = look up / flight-sim style) and make FSR1 disable MSAA on
enable, matching FSR2 behaviour (FSR provides its own spatial AA).

assets/shaders/fsr2_sharpen.frag.glsl

@@ -10,9 +10,7 @@ layout(push_constant) uniform PushConstants {
 } pc;
 
 void main() {
-    // Undo the vertex shader Y flip (postprocess.vert flips for Vulkan overlay,
+    vec2 tc = TexCoord;
-    // but we need standard UV coords for texture sampling)
-    vec2 tc = vec2(TexCoord.x, 1.0 - TexCoord.y);
 
     vec2 texelSize = pc.params.xy;
     float sharpness = pc.params.z;

assets/shaders/fsr_easu.frag.glsl

@@ -21,9 +21,7 @@ vec3 fsrFetch(vec2 p, vec2 off) {
 }
 
 void main() {
-    // Undo the vertex shader Y flip (postprocess.vert flips for Vulkan overlay,
+    vec2 tc = TexCoord;
-    // but we need standard UV coords for texture sampling)
-    vec2 tc = vec2(TexCoord.x, 1.0 - TexCoord.y);
 
     // Map output pixel to input space
     vec2 pp = tc * fsr.con2.xy; // output pixel position

include/rendering/camera_controller.hpp

@@ -162,7 +162,7 @@ private:
 
     // Mouse settings
     float mouseSensitivity = 0.2f;
-    bool invertMouse = false;
+    bool invertMouse = true;
     bool mouseButtonDown = false;
     bool leftMouseDown = false;
     bool rightMouseDown = false;

src/rendering/renderer.cpp

@@ -3865,7 +3865,13 @@ void Renderer::setFSREnabled(bool enabled) {
     if (fsr_.enabled == enabled) return;
     fsr_.enabled = enabled;
 
-    if (!enabled) {
+    if (enabled) {
+        // FSR1 upscaling renders its own AA — disable MSAA to avoid redundant work
+        if (vkCtx && vkCtx->getMsaaSamples() > VK_SAMPLE_COUNT_1_BIT) {
+            pendingMsaaSamples_ = VK_SAMPLE_COUNT_1_BIT;
+            msaaChangePending_ = true;
+        }
+    } else {
         // Defer destruction to next beginFrame() — can't destroy mid-render
         fsr_.needsRecreate = true;
     }