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>

tools/oracle/crypto.py

@@ -215,3 +215,35 @@ def ed25519_verify(public, msg, signature):
     except (InvalidSignature, ValueError):
         return False
     return True
+
+
+# --- did:key (W3C did:key method, multicodec and base58btc) ---------------------------
+
+BASE58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
+MULTICODEC = {"ed25519": 0xED, "ml-dsa-65": 0x1207}
+
+
+def _varint(n):
+    out = bytearray()
+    while True:
+        b = n & 0x7F
+        n >>= 7
+        out.append(b | (0x80 if n else 0))
+        if not n:
+            return bytes(out)
+
+
+def base58btc(data):
+    n = int.from_bytes(data, "big")
+    out = ""
+    while n:
+        n, r = divmod(n, 58)
+        out = BASE58[r] + out
+    return "1" * (len(data) - len(data.lstrip(b"\x00"))) + out
+
+
+def did_key(scheme, public):
+    """The did:key of a public key: `z` and the base58btc of the multicodec prefix and the key bytes."""
+    if scheme not in MULTICODEC:
+        raise ValueError("no multicodec code for " + scheme)
+    return "did:key:z" + base58btc(_varint(MULTICODEC[scheme]) + public)