Promote schema and canonicalizer out of history; add EvidenceModel (T06)

Verified the three published hashes reproduce byte for byte before promoting
anything, then moved the schema, canonicalizer and vectors into governed assets.
history/20260909-initial-exploration/ is untouched and stays the provenance
record.

- schemas/, informed_decision/, tests/vectors/ populated; the reference
  canonicalizer's ad-hoc __main__ block replaced by a real
  `python -m informed_decision` entry point.
- tests/test_canonicalize.py — 20 tests, all green. Published vectors, all four
  isolation properties, canonical-form round-trip, key sorting, and a provenance
  test asserting the governed fixtures have not drifted from history/.
- docs/specs/EvidenceModel.md — the two hashes, the split and why it exists, the
  four isolation properties, the presentation record, the bundle, and the
  relationship to audit-core.
- pyproject.toml, Makefile.

One test of mine was wrong on first run: it scanned for ", " to assert no
insignificant whitespace, which fires on prose inside a brief. Replaced with a
canonical round-trip comparison, which is the property actually meant. The
canonicalizer was correct.

EvidenceModel leads with what the model does NOT claim — no proof of
comprehension, no proof of reading (deliberately, since the alternative is
surveillance), no survival of a compromised surface, and audit-core's inherited
bound that a hash chain cannot prove a record was never sent.

T06 stays progress: the SCOPE.md rewrite is gated on the T02 ruling.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3W1dQG7GFFM9d94jFx7iR

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1565372@bnt-lap001
Assistant-Session: 16bb2f25-b34c-49ef-8e94-5fec3567a568

tests/vectors/adr-binding.json

@@ -0,0 +1,31 @@
+{
+  "memo_id": "01K4Q8Z3R7V2N6K9M1P5T8W4XC",
+  "memo_version": 2,
+  "question": "Do you formally accept ADR-0042 as the billing architecture for prod?",
+  "requested_act": "accept",
+  "binding_level": "aes",
+  "brief": "Replace nightly batch invoicing with an append-only event ledger.",
+  "locale": "en",
+  "ui_release": "informed-decision@0.3.1",
+  "packet": [
+    {
+      "item_id": "01K4Q8DOC0000000000000001",
+      "hash": {
+        "alg": "sha256",
+        "hex": "6b1c0f8a9d2e4c7b8a1f0e3d5c6b7a8f9e0d1c2b3a4f5e6d7c8b9a0f1e2d3c4b"
+      }
+    }
+  ],
+  "highlights": [
+    {
+      "id": "01K4Q8HL00000000000000001",
+      "item_id": "01K4Q8DOC0000000000000001",
+      "severity": "critical",
+      "required_ack": true,
+      "locator": {
+        "kind": "markdown_heading",
+        "heading": "Consequences / rollback"
+      }
+    }
+  ]
+}