feat: install tools/oracle as the paperspec package

Other repositories (paperstack, then paperpack) import the reference
implementation instead of reimplementing the specification; scienting-core
will take the role later behind the same vectors.

- pyproject.toml: distribution and import name `paperspec`, version 0.1.0,
  Python >= 3.12, no base dependencies; `tools/oracle` is the package, and
  `schemas/`, `sql/` and `vectors/` ship as the data subpackages
  `paperspec.schemas`, `paperspec.sql` and `paperspec.vectors`. Extras
  `schema`, `crypto` and `tools`.
- tools/oracle/__init__.py: the Python 3.14 and cryptography/jsonschema gate
  runs only when imported as `tools.oracle` by the repository's own tools.
- crypto.py imports `cryptography` on first use of HKDF and Ed25519, with an
  ImportError naming `paperspec[crypto]`; schema.py imports `jsonschema` and
  `referencing` in `Store.validator` and `Store.registry`. package.py, db.py
  and receipts.py then import on a bare interpreter.
- pixi.toml installs the package editable (pixi.lock re-solved; no conda pin
  changed), so the tools and the package resolve to the same code.
- tools/README.md names the library surface and the extras; CHANGELOG.md
  records the packaging change under 0.1.0, since check.py requires the
  changelog's first heading to equal the format version.

No computed value, vector, fixture, schema or SQL file changed.

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

tools/README.md

@@ -67,5 +67,8 @@ Hashes are kept incrementally.
 A node's five values depend only on its own subtree, so after a correction the oracle rehashes only the nodes that changed and their ancestors, and a container's projections are its children's cached projections joined.
 `check.py` compares the result after every correction with a slow computation that projects each node from its whole subtree.
 
-Do not build on it as a library.
-Implementations follow the [specification](../spec/README.md) and test themselves against the [vectors](../vectors/README.md).
+Other repositories of the project do not reimplement the specification: they install this repository as the Python package `paperspec` (`pip install .`, or a git pin) and import the oracle, so that every key, identifier, canonical JSON string, package check and database form comes from one piece of code.
+The library surface they use is `keys`, `text`, `jcs`, `package`, `db`, `schema` and `rights`, with the schemas, SQL and vectors as package data (`importlib.resources.files("paperspec") / "sql" / "doc.sql"`).
+Those modules run on Python 3.12 with the standard library alone, except that `schema` needs `paperspec[schema]` (`jsonschema` and `referencing`) and the HKDF and Ed25519 functions of `crypto` need `paperspec[crypto]`; `paperspec[tools]` installs both.
+When `scienting-core` exists it takes this role behind the same vectors, and the import changes without any computed value changing.
+Independent implementations follow the [specification](../spec/README.md) and test themselves against the [vectors](../vectors/README.md).