feat(licence): contributed manifests are CC0 1.0

Contributed manifests were in no declared condition at all, which left §9a
replication with no grant flowing through it: peers mirror each other's
catalogues wholesale, and every hop of that was unlicensed.

CC0 rather than a share-alike licence, because a share-alike works by asserting
a right in the data and then conditioning its use. The position in
docs/legal-posture.md §3 is that presence timings are facts rather than
protectable expression — asserting copyright in them in order to license them
would contradict that argument in the same repository, and that contradiction is
worth more to an opponent than the licence is worth to us. CC0 also waives the
sui generis database right by name, closing the EU-specific residual exposure
from the contributor's side.

The grant is taken at token issuance, and that is not incidental. There are no
accounts, so there is no sign-up to attach terms to, and a manifest arrives over
POST /manifests with no channel to negotiate over. Acquiring the contribute
capability is the only moment a grant can be made, so POST /tokens now returns
the licence and its terms alongside the token — a licence the server publishes
but never delivers is one no contributor agreed to.

The test pins the scope limit as well as the identifier. Bounding the grant to
the manifest is the half that can fail silently: a reworded term reading onto
the underlying work would purport to grant what no contributor can.

Also records the settled code-licence position across all four repositories in
the legal posture, correcting an earlier claim there that the plugin and
extraction repos declared nothing. Both already carried LICENSE files.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

TRACES: UR-019 | PR-006

README.md

@@ -10,6 +10,25 @@ point at it. If you are considering **running an instance**, read
 [`docs/legal-posture.md`](docs/legal-posture.md) first: it states what an
 instance holds, what it structurally cannot do, and the operator checklist.
 
+## Licensing — two licences, do not conflate them
+
+| | Licence | Where |
+|---|---|---|
+| **Code** | `GPL-3.0-or-later` | [`LICENSE`](LICENSE), declared in `Cargo.toml` |
+| **Contributed manifests** | **CC0 1.0 Universal** | [`LICENSE-DATA`](LICENSE-DATA), specified in [SPEC.md](SPEC.md) §5b |
+
+Both files ship with any distribution. They answer different questions, and a
+package carrying only `LICENSE` leaves the one that matters for federation
+unanswered.
+
+The data licence is the one that matters operationally, because manifests are
+what replicate between instances (§9a) — a code licence grants nothing over them.
+`POST /tokens` returns the licence and its terms with every issued token, so the
+grant is one contributors actually make rather than one the server announces.
+
+The grant covers **the manifest only** — timings, identifiers, audio signature.
+It does not, and cannot, license the underlying work.
+
 The community instance is **`https://jray.tourolle.paris`**. The JRay plugin
 ships with it pre-configured but **disabled** — §9 requires that no traffic leave
 an installation until an admin opts in, so the default entry exists to save the