Make main csound-free: remove render.sh + royal-road.csd + the csound tooling

Item 7 of the export queue. The entire csound era is preserved fully working on branch legacy-csound; main no longer carries any csound.

• royal-road.csd — the founding score (archived; still the origin story)

• tools/render.sh — the csound renderer

• tools/render-sung-melody.js — csound-dependent one-off (unreferenced)

• engine/faust/legacy-tools/ — the csound A/B harness (needs csound + buildCsd, both gone from main; its results live on in docs/history/ab-report.md, and the harness is recoverable from git history)

Verified: matrix 178/178, validate --quick PASS, engine ALL PASS.

▶ Play it: Rail Replacement Rapture — a bed-heavy genre where the found-sound layer carries the room https://stellate.app/?genre=transitwave&seed=9384&path=749.12536,768.12569,730.12569&xdur=13.122

5724245 https://github.com/aboard-io/stellate/commit/572424509e8b10be98c0d5d1518a98b0ea94aeec