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>

spec/18-layers.md

@@ -12,7 +12,7 @@ If it is about reading this paper, it belongs in a layer, where it is attributed
 ## 18.2 The layer
 
 A layer is a folder with `layer.json` and `annotations.jsonl`.
-`layer.json` is an `AnnotationCollection` with the two contexts, `format`, an `id` of the form `urn:scienting:layer:<store>/<record id>`, a `label`, a `purpose`, an `audience` (`novice`, `student`, `expert` or `mixed`), a `visibility` (`private`, `team` or `public`), a `license` (CC BY 4.0 by default when public), its `creator`, `created`, its `project`, the `docs` it annotates and its `total`.
+`layer.json` is an `AnnotationCollection` with the two contexts, `format`, an `id` of the form `tag:scient.ing,2026:layer:<store>/<record id>`, a `label`, a `purpose`, an `audience` (`novice`, `student`, `expert` or `mixed`), a `visibility` (`private`, `team` or `public`), a `license` (CC BY 4.0 by default when public), its `creator`, `created`, its `project`, the `docs` it annotates and its `total`.
 A reader turns layers on and off, and the audience dial picks the level of glosses.
 
 ## 18.3 The annotation
@@ -22,12 +22,12 @@ Each line of `annotations.jsonl` is a W3C `Annotation`:
 | Property | Holds |
 | --- | --- |
 | `@context` | `["http://www.w3.org/ns/anno.jsonld", "https://paperspec.scient.ing/context/scienting-1.jsonld"]`. |
-| `id` | `urn:scienting:annotation:<store>/<record id>` ([4.6](04-identity.md#46-record-ids)). |
+| `id` | `tag:scient.ing,2026:annotation:<store>/<record id>` ([4.6](04-identity.md#46-record-ids)). |
 | `type`, `layer` | `Annotation`, and the layer's ID. |
 | `motivation` | A W3C motivation: `commenting`, `describing`, `linking`, `questioning`, `assessing`, `replying` and the others. |
 | `creator`, `created`, `modified` | An agent `{id, type, name}`, with `type` `Person` or `Software`, and times. |
 | `body` | One body ([18.4](#184-bodies)). |
-| `target` | A `SpecificResource` whose `source` is `urn:scienting:doc:<store>/<key>` and whose `selector` lists an `AnchorSelector` holding a `scienting-anchor/1`, optionally followed by a W3C `TextQuoteSelector` for tools that do not know ours; or, for a reply, a `SpecificResource` whose source is another annotation. |
+| `target` | A `SpecificResource` whose `source` is `tag:scient.ing,2026:doc:<store>/<key>` and whose `selector` lists an `AnchorSelector` holding a `scienting-anchor/1`, optionally followed by a W3C `TextQuoteSelector` for tools that do not know ours; or, for a reply, a `SpecificResource` whose source is another annotation. |
 | `status` | `proposed`, `confirmed`, `rejected` or `withdrawn`. A model's annotation is `proposed` until a person confirms it. |
 | `receipt` | For a confirmed annotation, the receipt that covers it. |