- Add compile_deepsea_shader() with animated underwater-like GLSL shader
- Add render_deepsea_to_fbo() to render background to scene FBO
- Deep Sea shader features: FBM noise, animated blobs, caustic lines, vignette
- Add deepsea_program to cleanup() for proper resource management
- Add 2 new tests for Deep Sea shader compilation and FBO rendering
Task: Phase 1, Task 2 of frosted_glass_20260313 track
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