feat(rendering): implement RenderTexture base infrastructure and UIFrame clipping (#6)

- Added RenderTexture support to UIDrawable base class
  - std::unique_ptr<sf::RenderTexture> for opt-in rendering
  - Dirty flag system for optimization
  - enableRenderTexture() and markDirty() methods

- Implemented clip_children property for UIFrame
  - Python-accessible boolean property
  - Automatic RenderTexture creation when enabled
  - Proper coordinate transformation for nested frames

- Updated UIFrame::render() for clipping support
  - Renders to RenderTexture when clip_children=true
  - Handles nested clipping correctly
  - Only re-renders when dirty flag is set

- Added comprehensive dirty flag propagation
  - All property setters mark frame as dirty
  - Size changes recreate RenderTexture
  - Animation system integration

- Created tests for clipping functionality
  - Basic clipping test with visual verification
  - Advanced nested clipping test
  - Dynamic resize handling test

This is Phase 1 of the RenderTexture overhaul, providing the foundation
for advanced rendering effects like blur, glow, and viewport rendering.

ALPHA_STREAMLINE_WORKLOG.md

@@ -1,5 +1,76 @@
 # Alpha Streamline 2 Work Log
 
+## Phase 6: Rendering Revolution
+
+### Task: RenderTexture Base Infrastructure (#6 - Part 1)
+
+**Status**: Completed
+**Date**: 2025-07-06
+
+**Goal**: Implement opt-in RenderTexture support in UIDrawable base class and enable clipping for UIFrame
+
+**Implementation**:
+1. Added RenderTexture infrastructure to UIDrawable:
+   - `std::unique_ptr<sf::RenderTexture> render_texture`
+   - `sf::Sprite render_sprite`
+   - `bool use_render_texture` and `bool render_dirty` flags
+   - `enableRenderTexture()` and `markDirty()` methods
+2. Implemented clip_children property for UIFrame:
+   - Python property getter/setter
+   - Automatic RenderTexture creation when enabled
+   - Proper handling of nested render contexts
+3. Updated UIFrame::render() to support clipping:
+   - Renders frame and children to RenderTexture when clipping enabled
+   - Handles coordinate transformations correctly
+   - Optimizes by only re-rendering when dirty
+4. Added dirty flag propagation:
+   - All property setters call markDirty()
+   - Size changes recreate RenderTexture
+   - Animation system integration
+
+**Technical Details**:
+- RenderTexture created lazily on first use
+- Size matches frame dimensions, recreated on resize
+- Children rendered at local coordinates (0,0) in texture
+- Final texture drawn at frame's world position
+- Transparent background preserves alpha blending
+
+**Test Results**:
+- Basic clipping works correctly - children are clipped to parent bounds
+- Nested clipping (frames within frames) works properly
+- Dynamic resizing recreates RenderTexture as needed
+- No performance regression for non-clipped frames
+- Memory usage reasonable (textures only created when needed)
+
+**Result**: Foundation laid for advanced rendering features. UIFrame can now clip children to bounds, enabling professional UI layouts. Architecture supports future effects like blur, glow, and shaders.
+
+---
+
+### Task: Grid Background Colors (#50)
+
+**Status**: Completed  
+**Date**: 2025-07-06
+
+**Goal**: Add customizable background color to UIGrid
+
+**Implementation**:
+1. Added `sf::Color background_color` member to UIGrid class
+2. Implemented Python property getter/setter for background_color
+3. Updated UIGrid::render() to clear RenderTexture with background color
+4. Added animation support for individual color components:
+   - background_color.r, background_color.g, background_color.b, background_color.a
+5. Default background color set to dark gray (8, 8, 8, 255)
+
+**Test Results**:
+- Background color properly renders behind grid content
+- Python property access works correctly
+- Color animation would work with Animation system
+- No performance impact
+
+**Result**: Quick win completed. Grids now have customizable background colors, improving visual flexibility for game developers.
+
+---
+
 ## Phase 5: Window/Scene Architecture
 
 ### Task: Window Object Singleton (#34)