feat: publish the package from CI, and clean up its references

Publishing
- .gitea/workflows/publish.yml publishes paperspec to the instance's PyPI
  registry (/api/packages/infra/pypi) when a v* tag is pushed: it checks
  the repository, builds the sdist and wheel, refuses to upload unless the
  built version equals the tag, runs twine check --strict, and uploads
  with the secrets PACKAGE_USER and PACKAGE_TOKEN (--skip-existing, so a
  rerun on the same tag is safe). Run by hand, it refuses anything but a
  tag.
- pixi dev environment: twine >= 6.1 (the first that reads Metadata 2.4),
  and `dist` (sdist and wheel) replaces the `wheel` task.
- deploy/README.md: how to set up the secrets, release a version, and
  install from the registry with pixi, uv or pip, tying paperspec to the
  registry where the installer allows it.
- CONTRIBUTING.md "Releasing": a tag versions the package; a format
  change takes the new format version as the top CHANGELOG heading, and a
  code-only release takes the next patch as a subsection, as 0.1.1 does.
- pyproject: fallback_version 0+unknown for source trees without git; the
  license expression is Apache-2.0 AND CC0-1.0, for the code and the data
  the wheel carries.

Cleanup (from an audit of every reference to the package)
- spec/00 lists src/ (the package) and tools/ (how to run it), and no
  longer says the reference implementation is not a library.
- Stale explanations fixed in pixi.toml, .gitignore, the Caddyfile, the
  vectors, context, sql and tools READMEs, docs/examples.md, docs/faq.md,
  spec/01, docs/rationale.md and docs/comparison.md: the commands, what
  they need (the tools extra), the fixture folder hale2026harmonic-damb,
  and three lines that held two sentences.
- tools/README.md counts all six commands, says what needs which extra
  (package.validate and corrections.gate need [schema]), and that the
  vectors ship but the fixtures they name do not.
- The CLI's install and clone hints point at the registry instructions and
  an https clone URL; schema.py raises an ImportError naming
  paperspec[schema], as crypto.py does for [crypto].
- check's Unicode check now guards the package's pinned constant.
- site skips build/, dist/ and *.egg-info.
- CHANGELOG 0.1.1 describes the final state.

pixi run check passes (as `python -m paperspec check`); the rebuild is
byte-identical. pixi.lock needs `pixi lock` for twine before pushing: the
publish workflow installs with --locked.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

context/README.md

@@ -96,11 +96,12 @@ Three of the nine fixture annotations have only an `AnchorSelector` (the section
 - Reader: Follow [chapter 6](../spec/06-anchors.md) to resolve an anchor.
   The file `vectors/resolve.jsonl` resolves seventeen anchors against `fixtures/packages/hale2026harmonic-damb` and gives every outcome.
 - JSON-LD processor: Use a JSON-LD 1.1 processor; the context relies on `@json` and `@version` 1.1.
-- Checker: `schemas/annotation.schema.json` and `schemas/layer.schema.json` validate the files. `paperspec check` also checks that each annotation's ID derives from its content and that the receipt at `fixtures/records/layer/receipt.json` covers each `confirmed` annotation.
+- Checker: `schemas/annotation.schema.json` and `schemas/layer.schema.json` validate the files.
+  `paperspec check` also checks that each annotation's ID derives from its content and that the receipt at `fixtures/records/layer/receipt.json` covers each `confirmed` annotation.
 
 The traps:
 
-- No test vector pins the context, and nothing in `tools/` reads `scienting-1.jsonld`.
+- No test vector pins the context, and nothing here runs a JSON-LD processor on it; `paperspec check` and `paperspec site` read only its term IRIs.
   The schemas require only that `@context` be an array of at least two non-empty strings; they do not check the URLs.
   A file with a wrong context can pass the checker and still expand wrongly.
 - `@context` is part of an annotation's content hash (the hash covers everything except `status`, `receipt` and `modified`).