release: v3.9.1 - the counter probe sends a fixed read-only APDU

- The probe no longer takes a caller-supplied `apdu`: it always sends the
  read-only SELECT MF (the counter advances on the packet's security
  acceptance whatever the applet answers - 6A86/6D00 are normal there), so
  no caller can turn the sync probe into a write.
- Version 3.9.1: server VERSION, pyproject.toml and the PWA header; sw cache
  simple-v357; docs/api.md and the repo AGENTS.md updated, and the workspace
  AGENTS.md gains the v3.9.1 history entry (its "Currently" line was stale at
  v3.7.1).

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.9.0"
+version = "3.9.1"
 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.