feat!: pin Python 3.14 and Unicode 16.0, and make the tools commands

Python and Unicode
- requires-python is >=3.14,<3.15: 3.14 is the only Python with the
  Unicode 16.0 data the specification pins (3.13 has 15.1, 3.15 has 17.0).
- `import paperspec` raises ImportError unless unicodedata reports
  paperspec.UNICODE_VERSION (16.0.0), so a source checkout or an install
  that bypasses requires-python cannot compute values on other data.

Commands
- tools/{check,build,validate,load,stress,site}.py move with history to
  src/paperspec/cli/ and install as paperspec-check, -build, -validate,
  -load, -stress and -site; each also runs as `python -m paperspec.cli.X`.
- paperspec.cli.require() exits with "install paperspec[tools]" when
  cryptography or jsonschema is missing; paperspec.cli.checkout() finds
  the repository the check, build, stress and site commands work on (the
  editable install's own checkout, else the one around the current
  folder) and exits with a message outside one. tools/__init__.py is gone.
- validate and load read the schemas and SQL through the new
  paperspec.resources.path(), which finds them in a wheel and in an
  editable install alike, so they work anywhere the package is installed.
- check runs the rebuild as `python -m paperspec.cli.build`.
- build still writes the provenance tool label "paperspec tools/build.py":
  it is part of every hashed and signed fixture.
- pixi tasks and the check workflow run the commands; tools/README.md
  documents them, and the other docs name the commands instead of paths.

License
- LICENSE.md gives `src/` Apache-2.0 alongside `tools/`. Since the
  previous commit moved the code to src/, no row had covered it.

pixi run check passes (run as `python -m paperspec.cli.check` with src/ on
the path, since this environment cannot install the entry points); the
byte-for-byte rebuild matches, so no fixture or vector changed.
pixi.lock still needs `pixi lock`.

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

pixi.toml

@@ -39,13 +39,13 @@ default = { solve-group = "default" }
 dev = { features = ["dev"], solve-group = "default" }
 
 [tasks]
-check = { cmd = "python tools/check.py", depends-on = [
+check = { cmd = "paperspec-check", depends-on = [
     "lint",
 ], description = "Check schemas, records, packages, vectors, a byte-for-byte rebuild, the SQL round trip, prose and links" }
-quick = { cmd = "python tools/check.py --quick", description = "Check everything except the byte-for-byte rebuild" }
-build = { cmd = "python tools/build.py", description = "Rebuild fixtures/ and vectors/ from fixtures/src/ and the oracle" }
+quick = { cmd = "paperspec-check --quick", description = "Check everything except the byte-for-byte rebuild" }
+build = { cmd = "paperspec-build", description = "Rebuild fixtures/ and vectors/ from fixtures/src/ and the oracle" }
 lint = { cmd = "markdownlint-cli2", description = "Lint every Markdown file with markdownlint" }
-load = { cmd = "python tools/load.py", description = "Load packages into SQLite: pixi run load --sqlite lab.db PACKAGE..." }
-validate = { cmd = "python tools/validate.py", description = "Validate packages, or run proposed corrections through the gate" }
-stress = { cmd = "python tools/stress.py", description = "Stress the oracle with random inputs: pixi run stress -- --seed N" }
-site = { cmd = "python tools/site.py", description = "Build the website into _site/" }
+load = { cmd = "paperspec-load", description = "Load packages into SQLite: pixi run load --sqlite lab.db PACKAGE..." }
+validate = { cmd = "paperspec-validate", description = "Validate packages, or run proposed corrections through the gate" }
+stress = { cmd = "paperspec-stress", description = "Stress the oracle with random inputs: pixi run stress --seed N" }
+site = { cmd = "paperspec-site", description = "Build the website into _site/" }