[Test] (Diligent, MG_Test): add depth test and ensure default framebuffer isolation

- Verify nearer depth draw occludes farther draw
- Bind default framebuffer at test start so previous FBO state cannot leak
- Update handoff to 11 passing Diligent tests

HANDOFF_DILIGENT.md

@@ -103,6 +103,7 @@ Working tree is clean.
   - `DrawsToOffscreenFramebufferFromMobileGLState`
   - `DrawsWithScissorFromMobileGLState`
   - `DrawsWithBlendFromMobileGLState`
+  - `DrawsWithDepthTestFromMobileGLState`
 
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@@ -154,7 +155,7 @@ Verified locally on Turnip Adreno 750:
 - Local test result:
 
 ```
-[  PASSED  ] 10 tests
+[  PASSED  ] 11 tests
 ```
 
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@@ -245,7 +246,7 @@ Notes:
    - [x] Blend test
    - [x] Texture filtering / sampler state test
    - [x] framebuffer offscreen render-to-texture test
-   - [ ] Depth test visual test
+   - [x] Depth test visual test
    - [ ] Stencil test
 
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