test.yml: Use dorny/paths-filter to detect changed paths. Backend
tests only run when backend/**, biome.json, or the workflow itself
changes. Frontend build only runs when frontend/**, biome.json, or
the workflow changes. Jobs skipped via job-level 'if:' are treated
as passed by GitHub required checks.
codeql.yml: Only run on push/PR when JS/TS source files, package
files, or CodeQL config changes. Weekly schedule and manual dispatch
remain unfiltered.
Daniel Volz
2d9cd0ad1a