fix: pre-commit generate-images regex and regenerate README diagram

The YAML `>-` folding inserted a space in the `files:` regex, preventing
the hook from matching `statemachine/contrib/diagram/` paths. Use a
single-line string instead. Regenerate the README diagram with the green
state highlighted.

Author: fgmacedo

.pre-commit-config.yaml

@@ -40,9 +40,7 @@ repos:
       --events cycle cycle cycle
     language: system
     pass_filenames: false
-    files: >-
-      (statemachine/contrib/diagram/
-      |tests/examples/traffic_light_machine\.py)
+    files: (statemachine/contrib/diagram/|tests/examples/traffic_light_machine\.py)
   - id: pytest
     name: Pytest
     entry: uv run pytest -n auto --cov-fail-under=100