Tidy for export: single-page app, docs organized, dead code removed, README reset

Rename fallout + pre-export cleanup:

• Deleted the tombstone pages builder.html / play.html and the dead csound-era harnesses (faust/{index,ring-test,soak,insert-test,clicktest} + runners) and the now-orphaned faust/{bench,ring-conductor}.js

• Moved the completed planning docs (WAV-FIRST, KERNEL-V4, ZERO-STATIC, NEXT, EVALUATION, VALIDATION, ab-report) to docs/history/, keeping the architecture trail out of the root.

• Rewrote README.md from scratch for stellate as it is now (~110 genres, sampled-by-default + GM, per-voice Faust FX, the verifier loop, WAV-FIRST mobile, the CONSTELLATE explorer)

• CLAUDE.md / serve.sh / VOICES.md / legacy-tools updated for the rename and the current layout; all doc/page references fixed.

▶ Play it: Ballroom Leviathan — a horn-and-piano genre that plays almost entirely sampled instruments https://stellate.app/?genre=bigband&seed=3645&path=814.14134,833.14167,795.14167&xdur=13.122

3e5aa03 https://github.com/aboard-io/stellate/commit/3e5aa0359a66428090f00c1ee82239326e76011b