v3.22.1: rename the proactive action kind to proactive-drain

The kind string `proactive` read like an expectation of a proactive command
(`expect` is the step type for that) although the action consumes and answers
them.  Renamed everywhere:

- ACTION_KINDS / TEST_ACTION_KINDS (drift-tested), the normaliser branch and
  its error strings, the dispatch and the helper names (_test_run_drain,
  _drain_require_match/_label);
- the report label is DRAIN and the PWA summary reads "DRAIN x5 require ...
  TR ok";
- the editor/collect/summary/problem branches, docs/test-scripts.md
  (Proactive drain), docs/api.md, help EN/RU ("Очистка очереди proactive");
- the tests (TestRunnerProactiveDrain, the normalisation/data-check tests).

No stored scripts used the old kind (unpublished series), so there is no
alias and no migration.  sw cache simple-v404.
Tests: 839 frontend + 804 Python green.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.22.0"
+version = "3.22.1"
 description = "HTTP REST server wrapping pysim for the SIMple PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.