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>

pixi.toml

@@ -20,6 +20,11 @@ markdownlint-cli2 = ">=0.23.3"
 nodejs = ">=22"
 cryptography = ">=46"
 
+# The tools import the oracle as `tools.oracle`; other programs install it as `paperspec`. The editable
+# self-install makes both resolve to the same code.
+[pypi-dependencies]
+paperspec = { path = ".", editable = true }
+
 [tasks]
 check = { cmd = "python tools/check.py", depends-on = [
     "lint",