docs: render isometric peripheral blocks

[SirEdvin]

Summary

• generate self-contained isometric block renders from the current top, side, and active front textures
• use those renders on the documentation overview and peripheral pages
• show each API signature once as the method heading

Verification

• npm run docs:test
• PATH=/tmp/opencode/digitalitems-docs-venv/bin:$PATH timeout 10m ../../gradlew generateDocs
• rasterized both generated SVGs to verify face transforms and clipping