feat(shader): Add Deep Sea background shader for BlurPipeline

- 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

tests/test_shader_manager.py

@@ -43,6 +43,37 @@ def test_blur_pipeline_compile_shaders():
   assert pipeline.h_blur_program is not None
   assert pipeline.v_blur_program is not None
 
+def test_blur_pipeline_render_deepsea_to_fbo():
+ with patch("src.shader_manager.gl") as mock_gl:
+  tex_counter = iter([10, 20, 30])
+  fbo_counter = iter([1, 2, 3])
+  mock_gl.glGenTextures.side_effect = lambda n: next(tex_counter)
+  mock_gl.glGenFramebuffers.side_effect = lambda n: next(fbo_counter)
+  mock_gl.glCreateProgram.return_value = 300
+  mock_gl.glCreateShader.return_value = 400
+  mock_gl.glGetShaderiv.return_value = mock_gl.GL_TRUE
+  mock_gl.glGetProgramiv.return_value = mock_gl.GL_TRUE
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.setup_fbos(800, 600)
+  pipeline.compile_deepsea_shader()
+  pipeline.render_deepsea_to_fbo(800, 600, 0.0)
+  assert mock_gl.glBindFramebuffer.called
+  assert mock_gl.glUseProgram.called
+  assert mock_gl.glDrawArrays.called
+
+def test_blur_pipeline_deepsea_shader_compilation():
+ with patch("src.shader_manager.gl") as mock_gl:
+  mock_gl.glCreateProgram.return_value = 500
+  mock_gl.glCreateShader.return_value = 600
+  mock_gl.glGetShaderiv.return_value = mock_gl.GL_TRUE
+  mock_gl.glGetProgramiv.return_value = mock_gl.GL_TRUE
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.compile_deepsea_shader()
+  assert mock_gl.glCreateProgram.called
+  assert pipeline.deepsea_program is not None
+
 def test_blur_pipeline_prepare_blur():
  with patch("src.shader_manager.gl") as mock_gl:
   mock_gl.glGenFramebuffers.return_value = None