fix: address review feedback — recipe engine robustness and correctness

- Bug: chicken-egg-ci create-per-file-issues was aliased to shellcheck-only
  function. Added generic playbook_lint_per_file() that handles any linter
  output format. Renamed action to lint-per-file.
- Bug: cascade-rebase fired retry-merge synchronously after async rebase.
  Removed retry-merge and re-approve from recipe — rebase settles, CI reruns,
  normal flow handles merge on subsequent cycle.
- Warning: jq calls on PR data lacked || true under set -euo pipefail. Fixed.
- Warning: playbook_rebase_pr and playbook_retrigger_ci incremented
  _PB_SUB_CREATED before confirming API success. Now check HTTP status code.
- Warning: Python import tomllib fails on < 3.11. Added try/except fallback
  to tomli package.
- Nit: failures_on_unchanged regex broadened to handle generic linter formats
  (file.sh:line:col patterns in addition to ShellCheck's "In file line N:").
- Info: match_recipe now logs Python stderr on error instead of silently
  falling back to generic recipe.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gardener/recipes/chicken-egg-ci.toml

@@ -17,8 +17,8 @@ action      = "make-step-non-blocking"
 description = "Make failing step non-blocking (|| true) in the PR"
 
 [[playbook]]
-action      = "create-per-file-issues"
-description = "Create per-file fix issues for pre-existing violations"
+action      = "lint-per-file"
+description = "Create per-file fix issues for pre-existing violations (generic linter support)"
 
 [[playbook]]
 action      = "create-followup-remove-bypass"