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

.devin/skills/devx-workflow/SKILL.md

@@ -12,7 +12,6 @@ Quick reference for devx tools when working on the devx repo itself.
 | Check CI status | `make devx-pr-status` or `make devx-pr-status PR=42 WAIT=1` |
 | Fetch CI failure logs | `make devx-pr-logs` or `make devx-pr-logs PR=42 JOB=quality TAIL=50` |
 | Add ready-to-merge label | `make devx-pr-label` or `make devx-pr-label PR=42` |
-| Post PR review | `make devx-pr-review PR=42 EVENT=APPROVE BODY="..." CHECKLIST=1,2,3,4,5,6,7,8,9,10,11,12,13` |
 | Rebase current branch | `make rebase` |
 | Rebase PR via API | `make pr-rebase` or `make pr-rebase PR=42` |
 
@@ -24,6 +23,15 @@ When the `ready-to-merge` label is added and all CI checks pass:
 3. The rebase triggers a new CI run; the next auto-merge attempt merges
 4. No manual rebase needed unless the API rebase fails
 
+## Spec-Driven CI Gates (Pre-merge)
+
+Every PR must pass these gates before merge:
+
+| Gate | Module | What it checks |
+|------|--------|----------------|
+| Spec validation | `devx.ci.validate_spec` | Spec file exists at `docs/specs/<TASK-ID>.md`, has REQ-IDs, all ACs checked |
+| PR size | `devx.ci.check_pr_size` | Max 500 lines / 10 files (excludes CHANGELOG, badges, locks) |
+
 ## Key Rules
 
 - Never manually merge via API — always use auto-merge with `ready-to-merge` label