Unify rasterization with optimized capsule SDF

[jserv]

This consolidates line and path rendering across all ports (headless, WASM) to use capsule SDF algorithm matching SDL2's geometry-based rendering.

• Remove redundant algorithms: Xiaolin Wu, sharpened Wu, Bresenham
• Simplify iui_raster_line() to delegate to iui_raster_capsule()
• Add iui_raster_path_stroke() for consistent font rendering
• Remove unused iui_raster_cap() (capsule geometry includes caps)

Performance optimizations:

• Squared distance early-out avoids sqrtf for solid core pixels
• Adaptive AA fringe (0.35-0.5) for crisper thin lines
• Incremental dot product computation in inner loop
• Direct framebuffer access with pre-clipped bounds
• Row pointer caching for better memory access