Implement TREV-WP-0002 Stage 0 foundation: schemas, pure fold, golden Phase

Delivers the offline runnable specification foundation for the Trust Layer
(TSD §3-§6), not a hosted Trust Service:

- JSON Schemas for Phase Manifest, Ledger Entry, Extension Contract, and
  Conversion Attestation, encoding the Stage 0 working defaults (Q3 future
  license enum, Q6 single-currency Phases, Q8 required longstop_at).
- src/target_revenue: pure Outstanding Target fold, SHA-256 hash-chain
  verification, Ed25519 signing helpers, extension conformance checks
  (including a core-term-redefinition heuristic), and conversion detection
  that never requires an attestation document to determine conversion status.
- examples/phase-001: golden Phase package matching the concept doc's
  worked example, generated via scripts/generate_golden_phase.py so the
  hash chain is computed by the library itself, not hand-typed.
- 32 passing pytest tests covering manifest/ledger/extension conformance,
  tamper/reorder detection, and the full lifecycle fold to conversion.
- docs/adr/ADR-0001: proposed (not accepted) Stage 0 stack choice, per the
  WP-0002-T01 human-accept gate — implementation proceeded against the
  proposal as the workplan note permits, but the task stays open.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/phase-001/extensions/phase-sponsorship.json

@@ -0,0 +1,23 @@
+{
+  "id": "trsl:extension:phase-sponsorship",
+  "version": "1.0",
+  "value": {
+    "description": "Financial support explicitly directed at a named Phase, rather than the project generally."
+  },
+  "pricing": {
+    "method": "declared-amount, negotiated per sponsorship agreement"
+  },
+  "allocation": {
+    "rule": "The sponsoring party and the licensor explicitly declare the development_allocation fraction of the sponsorship amount at the time the sponsorship is recorded. Unrestricted general project sponsorship is not assigned to any Phase by default."
+  },
+  "recognition": {
+    "event": "payment-settled"
+  },
+  "reversal": {
+    "rule": "A withdrawn or refunded sponsorship generates a compensating credit-reversal entry for the previously declared development_allocation."
+  },
+  "evidence": {
+    "requirement": "Sponsorship agreement or written declaration stating the target Phase and declared allocation, plus settled payment reference."
+  },
+  "status": "registered"
+}