Poisson Prove 0.2.2

A release of the docs alone: the package's code is the same as 0.2.1's.

Added

• A new page, docs/what-a-declaration-checks.md: what a [declare] table records, stamps and
  prints, and what never reached means and does not. It held the second half of
  docs/what-capture-stores.md before, and the sweep spec now links to it for what steps and
  gates report.

Changed

• docs/recipes/in-ci.md gives every file a GitHub repository needs to gate its pull requests on
  Prove. make_comment.py is given in full: it reads the check --json file named on its command
  line and prints the comment, and an empty file, which a refused check leaves, gets a comment
  that says so. The main branch's workflow, prove-baseline.yml, is given in full beside the pull
  request's, prove.yml, which now also posts the comment. Every action in both is pinned to a
  full commit SHA. One line says that unresolved and timeout are the support bot's events, an
  example: on the quickstart's runs unresolved is refused with exit 1, so name your own.
• docs/artifact-format.md and docs/what-capture-stores.md are in short sections under headings
  you can jump by, with lists and tables where a paragraph listed, and an example of each stored
  format a paragraph describes, from a real run. No fact was cut.