perf(gl): drop the unused depth/stencil buffers from window and FBOs

The GL window asked for a 24-bit depth and 8-bit stencil buffer, and
every acrylic Framebuffer attached a DEPTH24_STENCIL8 renderbuffer the
size of its color texture. Nothing uses them: no code enables depth or
stencil tests (the ImGui GL3 backend disables both), every blit and
readback is color-only, and only Framebuffer::clear() also cleared the
depth buffer, which nothing read. The window and every FBO, including
the full-size capture FBO, carried that memory, and the FBO
renderbuffers were reallocated on every resize.

Now:
- the window requests depth 0 and stencil 0 explicitly (SDL3 requests a
  depth buffer by default when the attributes are simply removed);
  alpha 8 stays for the transparent window;
- Framebuffer has no renderbuffer, and clear() clears color only;
- a permanent startup log line,
  "GL default framebuffer: depth=N stencil=N", reports what the driver
  provided; "(no attachment)" marks a failed query, which is how some
  drivers report a buffer that does not exist.

The log shows depth=0 stencil=0 both offscreen and on WSLg X11, where
"Window transparency enabled by compositor" is still logged, with no
framebuffer-incomplete errors. Screenshot sweeps at 1280x720 and
2560x1440, and a glass run with ui_opacity 0.6 and blur on (so panels go
through the FBO blur), match the previous build within noise. The
driver-side memory saving itself was not measured. DX11 is unaffected:
its swap chain has no depth buffer.

Not verifiable here: macOS (an NSOpenGL 3.2 core context with a
transparent window).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.cpp

@@ -1233,8 +1233,9 @@ int main(int argc, char* argv[])
 
     // Create window with graphics context
     SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
-    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
+    // Nothing in the app uses depth/stencil (ImGui + acrylic are color-only): request none.
-    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
+    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
     SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 
     SDL_WindowFlags window_flags = (SDL_WindowFlags)(SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIGH_PIXEL_DENSITY | SDL_WINDOW_TRANSPARENT);
@@ -1268,6 +1269,11 @@ int main(int argc, char* argv[])
     }
 
     SDL_GL_MakeCurrent(window, gl_context);
+    { int d = -1, s = -1;
+      const bool okd = SDL_GL_GetAttribute(SDL_GL_DEPTH_SIZE, &d);
+      const bool oks = SDL_GL_GetAttribute(SDL_GL_STENCIL_SIZE, &s);
+      DEBUG_LOGF("GL default framebuffer: depth=%d%s stencil=%d%s\n",
+                 d, okd ? "" : " (no attachment)", s, oks ? "" : " (no attachment)"); }
     SDL_GL_SetSwapInterval(1); // Enable vsync
 
     bool backdrop_active = false;

src/ui/effects/framebuffer.cpp

@@ -35,14 +35,12 @@ Framebuffer::~Framebuffer()
 Framebuffer::Framebuffer(Framebuffer&& other) noexcept
     : fbo_(other.fbo_)
     , colorTexture_(other.colorTexture_)
-    , depthRbo_(other.depthRbo_)
     , width_(other.width_)
     , height_(other.height_)
     , isComplete_(other.isComplete_)
 {
     other.fbo_ = 0;
     other.colorTexture_ = 0;
-    other.depthRbo_ = 0;
     other.width_ = 0;
     other.height_ = 0;
     other.isComplete_ = false;
@@ -55,14 +53,12 @@ Framebuffer& Framebuffer::operator=(Framebuffer&& other) noexcept
         
         fbo_ = other.fbo_;
         colorTexture_ = other.colorTexture_;
-        depthRbo_ = other.depthRbo_;
         width_ = other.width_;
         height_ = other.height_;
         isComplete_ = other.isComplete_;
         
         other.fbo_ = 0;
         other.colorTexture_ = 0;
-        other.depthRbo_ = 0;
         other.width_ = 0;
         other.height_ = 0;
         other.isComplete_ = false;
@@ -104,19 +100,12 @@ bool Framebuffer::init(int width, int height, bool useFloat16)
     // Attach color texture to framebuffer
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, colorTexture_, 0);
     
-    // Create depth renderbuffer (optional, but good for completeness)
-    glGenRenderbuffers(1, &depthRbo_);
-    glBindRenderbuffer(GL_RENDERBUFFER, depthRbo_);
-    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, width, height);
-    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depthRbo_);
-    
     // Check completeness
     isComplete_ = checkComplete();
     
     // Unbind
     glBindFramebuffer(GL_FRAMEBUFFER, 0);
     glBindTexture(GL_TEXTURE_2D, 0);
-    glBindRenderbuffer(GL_RENDERBUFFER, 0);
     
     if (!isComplete_) {
         DEBUG_LOGF("Framebuffer::init - Framebuffer is not complete!\n");
@@ -146,10 +135,6 @@ void Framebuffer::cleanup()
         glDeleteTextures(1, &colorTexture_);
         colorTexture_ = 0;
     }
-    if (depthRbo_) {
-        glDeleteRenderbuffers(1, &depthRbo_);
-        depthRbo_ = 0;
-    }
     if (fbo_) {
         glDeleteFramebuffers(1, &fbo_);
         fbo_ = 0;
@@ -194,7 +179,7 @@ void Framebuffer::unbind()
 void Framebuffer::clear(float r, float g, float b, float a)
 {
     glClearColor(r, g, b, a);
-    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+    glClear(GL_COLOR_BUFFER_BIT);
 }
 
 void Framebuffer::blitFrom(GLuint srcFbo, int srcX, int srcY, int srcWidth, int srcHeight,

src/ui/effects/framebuffer.h

@@ -125,7 +125,6 @@ private:
     
     GLuint fbo_ = 0;
     GLuint colorTexture_ = 0;
-    GLuint depthRbo_ = 0;  // Renderbuffer for depth (optional)
     
     int width_ = 0;
     int height_ = 0;