DEVX-155: Replace pr_review with spec-driven CI gates and pr-review skill

.devin/skills/testing-and-debugging/SKILL.md

@@ -45,6 +45,13 @@ This runs `lint-all` + `pytest-cov`. The pre-push git hook only
 validates the Vikunja task exists — it does NOT run tests. You must
 run `make pre-push` manually.
 
+### Spec-Driven Workflow
+
+Every PR requires a spec file at `docs/specs/<TASK-ID>.md`. See the
+`spec-driven-development` skill for the full workflow and template.
+CI validates the spec (via `devx.ci.validate_spec`) and checks PR size
+(via `devx.ci.check_pr_size`) before running expensive jobs.
+
 ## CI Failure Investigation
 
 When investigating a CI failure: