Metabolism: song as substrate, ecology grown from the track

A new top-level section building the metabolism concept: the track
supplies the food field, event impulses and per-section laws; the seed
picks the species (a rule set, not a parameter vector). Same song + seed
=> bit-identical frames; different songs => different worlds.

- analysis: single FFT pass -> per-frame feature table; score (onsets
  folded into world geometry via voice ring + pitch-class sector), wells
  (food placed by the harmony), graph (band correlations -> interaction
  matrix), laws (per-section regimes)
- sim: typed-array world, 3 castes (builder/orbit, forager/commute,
  spark/orbit-wide) with causality rings, persistence trails,
  consequence field; fully deterministic
- lens: software framebuffer renderer (PNG in node, ImageData in
  browser) + event-reactive camera (cuts on activity change, alternating
  shot sizes, drift-and-push)
- metrics: coupling x residual fitness (not per-frame descriptors) plus
  a grown-structure fingerprint; report + strip tools; 15 tests green
- DESIGN.md captures the concept, invariants and build order

3 reference test signals (drone/runner/dusk) grow measurably distinct
worlds while seeds of one song stay in the same biome.

metabolism/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "metabolism",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "description": "Songs as substrate: agent ecologies whose laws are derived from the track, rendered deterministically.",
+  "scripts": {
+    "dev": "vite",
+    "test": "node --test test/*.test.js",
+    "strip": "node tools/strip.js",
+    "report": "node tools/report.js"
+  },
+  "devDependencies": {
+    "vite": "^7.2.2"
+  }
+}