Form grammar: seven forms as data, optional intro, section-drop lever

Stage 1 — the seven-branch buildSections if/else chain is now a FORMS data table walked by one generic buildForm. Nodes are [name, spec] pairs typed via sectionTag

• Stage 2a — introMode (Paul: "four bar intro almost everywhere — make it optional"): zero-rng dominant-parent enum

• Stage 2b — section-drop solver lever: when cycle-flooring lands over-band, drop optional low-energy nodes (never build/peak/hook), commit ONLY if the result lands in [162,198]s, else revert byte-identical.

• Stage 3 — generateSong DELETED: defaultState inlined as the value-identical royal-road literal; render-sample-video's synthwave preset inlined value-identical (vaporwave preset stays on defaultState

Verified: verify.sh --full --no-cache PASS; walker 0.219 ms/track vs 0.225 baseline (no regression); rng streams untouched, proven by the 47 untouched genres' byte-stability.

▶ Play it: Jackhammer Communion → Food Court Eternity → Highway Heat Death — the three genres this change names, as one path https://stellate.app/?genre=gabber&seed=8461&path=1809.17533,1679.4415,859.9931&xdur=0.057

c0e7cbc https://github.com/aboard-io/stellate/commit/c0e7cbcdcd3be8759f1af9480362598daf3d831e