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>

pyproject.toml

@@ -7,7 +7,8 @@ name = "paperspec"
 dynamic = ["version"]
 description = "The scienting formats: the reference implementation of every rule, with the JSON Schemas, SQL and test vectors as package data"
 readme = "README.md"
-license = "Apache-2.0"
+# The code (src/) is Apache-2.0 and the schemas, SQL and vectors it carries are CC0-1.0, as LICENSE.md says.
+license = "Apache-2.0 AND CC0-1.0"
 license-files = ["LICENSE.md"]
 authors = [{ name = "Scientific Computing Studio", email = "maintainer@scient.ing" }]
 # Python 3.14 is the only version with the Unicode 16.0 character data the specification pins (spec/01 §1.4);
@@ -57,9 +58,11 @@ packages = ["paperspec", "paperspec.cli", "paperspec.schemas", "paperspec.sql",
 "paperspec.sql" = ["*.sql"]
 "paperspec.vectors" = ["*.jsonl"]
 
-# The package version comes from git tags (v0.1.0 builds as 0.1.0, later commits as 0.1.1.devN). It is the
-# version of this code, not of the formats, which CHANGELOG.md and pixi.toml carry.
+# The package version comes from git tags (v0.1.1 builds as 0.1.1, later commits as 0.1.2.devN); CONTRIBUTING.md
+# says how it relates to the format version that CHANGELOG.md and pixi.toml carry. A source tree without git
+# history, such as a downloaded archive, builds as 0+unknown instead of failing.
 [tool.setuptools_scm]
+fallback_version = "0+unknown"
 version_file = "src/paperspec/_version.py"
 version_scheme = "guess-next-dev"
 local_scheme = "node-and-timestamp"