feat(shader): Add BlurPipeline class for frosted glass FBO setup

- Add BlurPipeline class with downsampled FBO support (scene, blur_a, blur_b)
- Implement 2-pass Gaussian blur shaders (horizontal + vertical)
- Add setup_fbos(), compile_blur_shaders(), prepare_blur(), cleanup() methods
- Add tests for BlurPipeline initialization, FBO setup, shader compilation, blur execution, and cleanup

Task: Phase 1, Task 1 of frosted_glass_20260313 track

tests/test_shader_manager.py

@@ -1,6 +1,83 @@
 import pytest
 from unittest.mock import patch, MagicMock
 
+def test_blur_pipeline_import():
+ with patch("src.shader_manager.gl") as mock_gl:
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  assert pipeline is not None
+  assert pipeline.scene_fbo is None
+  assert pipeline.blur_fbo_a is None
+  assert pipeline.blur_fbo_b is None
+  assert pipeline.scene_tex is None
+  assert pipeline.blur_tex_a is None
+  assert pipeline.blur_tex_b is None
+  assert pipeline.h_blur_program is None
+  assert pipeline.v_blur_program is None
+
+def test_blur_pipeline_setup_fbos():
+ 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)
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.setup_fbos(800, 600)
+  assert mock_gl.glGenFramebuffers.called
+  assert mock_gl.glGenTextures.called
+  assert pipeline.scene_fbo is not None
+  assert pipeline.blur_fbo_a is not None
+  assert pipeline.blur_fbo_b is not None
+
+def test_blur_pipeline_compile_shaders():
+ with patch("src.shader_manager.gl") as mock_gl:
+  mock_gl.glCreateProgram.return_value = 100
+  mock_gl.glCreateShader.return_value = 200
+  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_blur_shaders()
+  assert mock_gl.glCreateProgram.called
+  assert pipeline.h_blur_program is not None
+  assert pipeline.v_blur_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
+  mock_gl.glGenTextures.return_value = None
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.scene_fbo = 1
+  pipeline.scene_tex = 10
+  pipeline.blur_fbo_a = 2
+  pipeline.blur_tex_a = 20
+  pipeline.blur_fbo_b = 3
+  pipeline.blur_tex_b = 30
+  pipeline.h_blur_program = 100
+  pipeline.v_blur_program = 101
+  pipeline.prepare_blur(800, 600, 0.0)
+  assert mock_gl.glBindFramebuffer.called
+  assert mock_gl.glUseProgram.called
+
+def test_blur_pipeline_cleanup():
+ with patch("src.shader_manager.gl") as mock_gl:
+  from src.shader_manager import BlurPipeline
+  pipeline = BlurPipeline()
+  pipeline.scene_fbo = 1
+  pipeline.blur_fbo_a = 2
+  pipeline.blur_fbo_b = 3
+  pipeline.scene_tex = 10
+  pipeline.blur_tex_a = 20
+  pipeline.blur_tex_b = 30
+  pipeline.h_blur_program = 100
+  pipeline.v_blur_program = 101
+  pipeline.cleanup()
+  assert mock_gl.glDeleteFramebuffers.called
+  assert mock_gl.glDeleteTextures.called
+  assert mock_gl.glDeleteProgram.called
+
 def test_shader_manager_initialization_and_compilation():
  # Import inside test to allow patching OpenGL before import if needed
  # In this case, we patch the OpenGL.GL functions used by ShaderManager