chore: harden audit checks and issue taxonomy

requirements-dev.txt

@@ -24,6 +24,7 @@
 -e ../govoplan-dataflow
 -e ../govoplan-workflow
 -e ../govoplan-views
+-e ../govoplan-postbox
 -e ../govoplan-poll
 -e ../govoplan-scheduling
 -e ../govoplan-notifications
@@ -37,6 +38,7 @@ idna>=3.15
 jsonschema>=4,<5
 pip>=26.1.2
 pip-audit>=2.9,<3
-pytest>=8,<9
+pytest>=9.0.3,<10
+pygments>=2.20,<3
 python-multipart>=0.0.31
 ruff>=0.14,<1