GRM-165: feat: adopt spec-driven CI gates, create_dependency_pr, and pr-review skill

Replace pr_review CI steps with validate_spec + check_pr_size + curl-based
APPROVE. Add create_dependency_pr step to post-merge for auto-creating infra
PR to bump grm version. Add spec-driven-development and pr-review skills.
Update AGENTS.md.

Implements: REQ-1, REQ-2, REQ-3, REQ-4

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

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

@@ -35,6 +35,12 @@ produces false failures (missing dependencies, wrong Python version).
 | All platforms | `make molecule-all` | All 6 scenarios on all 4 OSes |
 | Parallel | `make molecule-all-parallel` | MOLECULE_JOBS=4 |
 
+### 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 before running expensive jobs.
+
 ## Pre-Push Verification
 
 **Before pushing any branch:**