feat: minted keys, VRF seeds, RFC 9162 proofs, history roots, tag URIs and a transparency log

Keys (spec/02 §2.4), the rule paperstack settled on:
- A work key is a Scholar-style citation key, a hyphen and the first four
  Crockford base32 characters of SHA-256("scienting-key/1:" + identity),
  where the identity is the first of doi, arxiv, isbn, pmid, pmcid and
  openalex in same_as, else the folded title, year and family name. A
  collision lengthens the later key by two characters; a key is minted
  once and never recomputed. A document key adds .si, .v<seq> or .<type>
  for versions other than the version of record.
- Every fixture key is now minted (hale2026harmonic-damb,
  okafor2025solvent-acth, writer2027fixed-ynr7.v3, tiny2026tiny-j4qm), so
  every node and record ID was re-minted and the docs rewritten to match.
  The validator checks the document key against the work key and version
  (doc.key.work) and the hash part against the identifier (doc.key.suffix).
  vectors/keys.jsonl pins the cases paperstack's tests pin.

Review:
- Spot-check seeds are ECVRF-EDWARDS25519-SHA512-TAI proofs (RFC 9381),
  implemented in tools/oracle/vrf.py in plain Python and reproduced
  against the RFC's Example 16; the sample ranks by the VRF output. The
  earlier Ed25519 seed could be ground by a dishonest checker.
- RFC 9162 inclusion and consistency proofs (crypto.inclusion_path,
  verify_inclusion, consistency_proof, verify_consistency) with
  scienting-proof/1, vectors/proofs.jsonl and two fixture records.
- document.json carries `history`, the root over the corrections, with
  the empty-tree hash for none (spec/11 §11.5, rule doc.history).
- A provisional transparency log (spec/23): log entries, signed-note
  checkpoints with key hashes as transparency logs share them, the rule
  that a logged revocation beats a self-asserted time, and vectors.
- Reserved signature schemes cose and ml-dsa-65 (spec/08 §8.4).

Identifiers and text:
- urn:scienting: becomes tag:scient.ing,2026: (RFC 4151), since the URN
  namespace was never registered.
- Unicode 16.0 is pinned for normalization and categories (spec/01 §1.4);
  the checker refuses another version.

Checking:
- check.py: keys, proofs, VRF and checkpoint vectors; the proof and
  checkpoint records; a check that every ID and hash the prose quotes
  exists in the fixtures or vectors; three more broken packages
  (history-wrong, key-suffix, key-work).
- stress.py: key, VRF, proof and checkpoint properties.
- Docs: a keys section in the concepts and FAQ, rationale entries for
  keys, VRF, proofs, tag URIs and the Unicode pin, a "Looking ahead"
  section, media-type registration and OCI distribution notes.

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

registry/README.md

@@ -6,7 +6,7 @@ This page is for newcomers, implementers who need the exact behavior, and expert
 
 | File | Holds |
 | --- | --- |
-| `formats.json` | Every format: its identifier, media type (null for the five that have none), schema, status, chapter and a one-line description. |
+| `formats.json` | Every format: its identifier, media type (null for the six that have none), schema, status, chapter and a one-line description. |
 | `rules.json` | Every validation rule ID, with what it means and the chapter that defines it. |
 | `stamps/scienting-stamps-1.json` | The published rules that recognize the download stamps publishers add to PDFs (see Adding stamp rules), so page fingerprints ignore them. |
 | `stages/scienting-stages-default.json` | The rights each processing stage needs, as a default a team may replace. |
@@ -17,10 +17,17 @@ Each entry in `formats.json` has a `status`.
 A `candidate` format is complete, with vectors and fixtures, and ready to implement.
 It changes only with a recorded reason and a new or changed vector.
 A `provisional` format is complete and expected to change as implementations gain experience, so it may change more freely.
-At version 0.1.0, 18 of the 29 formats are `candidate` and 11 are `provisional`.
+At version 0.1.0, 19 of the 32 formats are `candidate` and 13 are `provisional`.
 The third defined value, `reserved`, is unused.
 The values are defined in [Chapter 0, section 0.4](../spec/00-introduction.md#04-status), and the stability rules in [Chapter 22, section 22.5](../spec/22-conformance.md#225-stability).
 
+## Registering the media types
+
+The `application/vnd.scienting.*` media types are vendor-tree types, which IANA registers on request without a standards document (RFC 6838 §3.2).
+Register each type the formats serve over the web before the first release that other tools read: the zipped package, the anchor, the receipt and the layer first.
+Until then the types are unregistered and work as they are; a registration changes no byte of any file.
+The JSON-LD context is `application/ld+json` and a checkpoint is `text/plain`, both already registered.
+
 ## Rule IDs
 
 A validator checks a package and reports each failure as `path:line: rule: message`, for example: