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>

tests/conftest.py

@@ -0,0 +1,28 @@
+import json
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+SRC = REPO_ROOT / "src"
+if str(SRC) not in sys.path:
+    sys.path.insert(0, str(SRC))
+
+EXAMPLES_DIR = REPO_ROOT / "examples" / "phase-001"
+FIXTURES_DIR = Path(__file__).resolve().parent / "fixtures"
+
+
+def load_json(path: Path) -> dict:
+    with open(path, encoding="utf-8") as f:
+        return json.load(f)
+
+
+def golden_manifest() -> dict:
+    return load_json(EXAMPLES_DIR / "manifest.json")
+
+
+def golden_entries() -> list[dict]:
+    return load_json(EXAMPLES_DIR / "ledger.json")
+
+
+def golden_extension(name: str) -> dict:
+    return load_json(EXAMPLES_DIR / "extensions" / f"{name}.json")