feat: ML-DSA-65, did:key, named hash algorithm, model provenance, log tiles and witnesses

- hashing.algorithm names the hash function in every document; a consumer refuses one it does not implement (doc.hash.algorithm)
- ML-DSA-65 (FIPS 204) is an implemented signature scheme: pure-Python reference in tools/oracle/mldsa.py checked against NIST ACVP vectors, a receipt signed by the new roster key dana, and signature vectors for key generation and a deterministic signature
- roster keys may carry a did:key, which the validator checks against the public key (doc.roster.did), and a witness purpose for parties that cosign log checkpoints
- model provenance: a correction's author and an annotation's generator name the model with provider, version and the hashes of its weights, prompt and parameters, and where it ran
- the transparency log gains the tlog-tiles static layout (fixtures/records/log/), a project settings.log with origin, witnesses and threshold, and an acceptance rule; the fixture checkpoint is cosigned by a witness
- store.sql: roster_keys accepts cose and ml-dsa-65 and gains a did column
- spec chapters 01, 08, 11, 18, 20 and 23, the rationale, glossary, fixture, vector and tool guides updated; stress harness covers ML-DSA

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

schemas/roster.schema.json

@@ -63,13 +63,19 @@
             "type": "string",
             "minLength": 1
           },
+          "did": {
+            "type": "string",
+            "pattern": "^did:key:z[1-9A-HJ-NP-Za-km-z]+$",
+            "description": "The key as a did:key decentralized identifier, which the public key determines (spec/08 §8.7)."
+          },
           "purposes": {
             "type": "array",
             "items": {
               "enum": [
                 "sign",
                 "spot-check",
-                "export"
+                "export",
+                "witness"
               ]
             },
             "minItems": 1,