Promote entire passepartout-economics/ to ideas/ root

All 31 files from ideas/passepartout-economics/ promoted to ideas/ root.
- Subfolder's passepartout-economics.org (42-line index) renamed to
  triad-index.org to avoid collision with root-level full doc
- index.org removed (redundant — triad-index.org replaces it)
- Root-level passepartout-economics.org: stripped file:passepartout-economics/
  prefix from all cross-references (now simple file:foo.org links)
- compliance-framework-mapping.org: same prefix cleanup
- All internal file: links within the economics docs already used simple
  names (no prefix) — they resolve correctly from ideas/ root

ideas/cost-structure.org

@@ -0,0 +1,14 @@
+:PROPERTIES:
+:ID:       0b5a8a74-cfd6-542d-bc88-4eb3cd8626f9
+:END:
+#+title: Cost Structure — Zero Marginal Cost
+#+filetags: :passepartout:economics:cost:marginal:zero:
+
+- **One-time cost:** [[file:gate-rule-encoding.org][gate-rule encoding]] for a domain (from hours for codified domains up to months for tacit domains)
+- **Near-zero marginal cost:** ACL2 proof + Screamer consistency check + VivaceGraph lookup per interaction — all CPU-native, all in-image
+- **No recurring LLM API costs** for the 80% symbolic reasoning layer
+- **After [[file:sufficiency-flip.org][sufficiency flip]]:** pennies per day vs dollars per day for LLM-only
+
+The cost curve inverts: generation is expensive, verification is cheap. This is the inversion Passepartout exploits. This is the core insight of [[file:lisp-economics.org][Lisp economics]] — symbolic verification costs approach zero while LLM token costs remain constant.
+
+Token demand shifts from "every interaction burns tokens" to "only unfamiliar interactions burn tokens." Steady-state per-user LLM consumption drops by an order of magnitude.