Rebuild architecture diagrams as hand-written draw.io style SVG

Hand-write SVG with draw.io visual style (colors, rounded corners,
foreignObject text, dark mode support) and manually calculated
orthogonal edge paths with arrowhead polygons. This approach
produces the best rendering quality on GitHub since draw.io MCP/CLI
SVG export doesn't include edge path data.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: haowu77