Check the signed-in markup from a scheduled workflow

Move the authenticated drift check into the repository as
tools/compat_auth.py, run daily by .github/workflows/compat-auth.yml on the
maintainer's forge only. Credentials come from FH_EMAIL and FH_PASSWORD, the
output is pass/fail labels only because the run log is public, and a failed
run pushes the report to ntfy. Exit 5 means all hold, 10 drift, anything
else that it could not run.

Point compat.yml, tools/compat.py and the docs at it, add a README section,
and cut 0.5.1.

custom_components/freshharvest/manifest.json

@@ -12,5 +12,5 @@
   "requirements": [
     "beautifulsoup4>=4.12"
   ],
-  "version": "0.5.0"
+  "version": "0.5.1"
 }