feat!: one paperspec command with subcommands, help and examples

The six console scripts (paperspec-check, -build, -validate, -load,
-stress, -site) become subcommands of a single `paperspec` command:
paperspec validate, load, check, build, stress and site. `python -m
paperspec COMMAND` runs the same thing.

- paperspec/cli/main.py builds the whole parser, apart from the commands,
  so `paperspec --help` and `paperspec COMMAND --help` work without a
  checkout or the tools extra; a command's module is imported only when
  it runs.
- `paperspec` with no command prints the overview: what each command does,
  examples, and which work anywhere (validate, load) and which need a
  checkout (check, build, stress, site). Each command's help has a
  description with advice, and worked examples; a misspelled command gets
  a suggestion (argparse suggest_on_error); `--version` prints the version
  and the pinned Unicode version.
- Each command module exposes run(args) and returns the exit status.
  Arguments that parse but do not fit together raise UsageError, which
  prints the command's usage and exits 2: load now also refuses
  --built-from or --store without --bundle.
- The failure messages say what to do: install paperspec[tools], clone the
  repository, rerun stress with the printed seed, or run paperspec build
  when the rebuild check differs. check and stress say how many failures
  they did not list.
- check runs the rebuild as `python -m paperspec build`.
- pyproject installs one script, `paperspec`; the pixi tasks and the docs
  use the subcommands.

pixi run check passes (run here as `python -m paperspec check` with src/ on
the path); the rebuild is byte-identical. pixi.lock still needs
`pixi lock`.

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

sql/README.md

@@ -31,7 +31,7 @@ dolt sql < sql/doc.sql && dolt sql < sql/store.sql
 The PostgreSQL database `lab` and the Dolt repository must already exist.
 The `sqlite3` line runs as shown; the `psql` and `dolt` lines follow the portability rules of [chapter 13](../spec/13-database.md#131-portability) but have not been run on those engines in this repository.
 
-To load packages into SQLite without pixi, install the package with its `tools` extra on Python 3.14, then run `paperspec-load --sqlite lab.db PACKAGE…`.
+To load packages into SQLite without pixi, install the package with its `tools` extra on Python 3.14, then run `paperspec load --sqlite lab.db PACKAGE…`.
 The file [docs/examples.md](../docs/examples.md#load-packages-into-sqlite) has queries to try.
 The loader copies files that have no table (assets, dataset files, derived files) by SHA-256 into `lab.db.assets/`.
 
@@ -57,7 +57,7 @@ On `fixtures/packages/hale2026harmonic-damb` it returns one row, `hca6dc5`: the
 - Names: no table, column or index name is reserved in SQLite, PostgreSQL or MySQL (Dolt is MySQL-compatible).
   The formats' `key`, `index`, `at`, `by`, `before` and `after` become `doc_key`, `idx`, `made_at`, `signer`, `before_hash` and `after_hash`.
 - Round trip: each row keeps every property of its record, so unloading restores the same bytes and the same manifest hash.
-  Unloading copies the files with no table from the asset store, which must travel with the database. `paperspec-check` tests this for every fixture package.
+  Unloading copies the files with no table from the asset store, which must travel with the database. `paperspec check` tests this for every fixture package.
 - Derived tables: `citations`, `receipt_nodes` and `annotation_targets` are built on load for queries and are not part of the package.
 
 ## Status