Auto-merge should work without merge queue — direct merge fallback

[Trecek]

Problem

The auto_merge ingredient (default "true") in implementation and remediation recipes is described as "Enroll the PR in the merge queue automatically after checks pass." This couples auto-merge to merge queue availability.

In route_queue_mode, when auto_merge == "true":

• If queue_available == true → enables auto-merge and waits for queue (enable_auto_merge → wait_for_queue)
• If queue_available == false → routes to release_issue_success (implementation) / confirm_cleanup (remediation) — PR is left unmerged

This means repos without a merge queue never get their PRs merged automatically, even though the recipe's intent is to merge after CI and review pass.

Desired Behavior

When auto_merge is "true", the recipe should merge the PR regardless of whether a merge queue exists:

1. Merge queue present: Current behavior — gh pr merge --squash --auto enrolls in the queue, wait_for_merge_queue polls until merged/ejected.
2. No merge queue: gh pr merge --squash --auto should still be called. GitHub handles this natively — --auto waits for required status checks then merges directly without needing a queue. The recipe should poll for merge completion (PR state = merged) rather than calling wait_for_merge_queue.

The merge queue is largely irrelevant to the agent workflow because:

• The agent already waits for CI and review to pass before attempting merge
• If a concurrent merge introduces a conflict, the agent can resolve it and re-push
• gh pr merge --squash --auto delegates queue-vs-direct to GitHub's branch ruleset automatically

Scope

• implementation.yaml: Update route_queue_mode to add a direct-merge path when queue_available == false instead of skipping to release_issue_success
• remediation.yaml: Same change — direct-merge path when no queue
• Ingredient description: Update auto_merge description from "Enroll the PR in the merge queue" to "Automatically merge the PR after checks pass"
• Merge completion polling: For the no-queue path, poll PR state for merged (similar to what merge-pr skill does with gh pr view --json state,mergedAt)
• Ejection/conflict handling: Ensure the no-queue path handles merge failures (e.g., conflict from concurrent merge) with the same resolve-and-retry pattern used in the queue path

Follows from #381 which added the auto_merge ingredient.

Requirements

ROUTE — Recipe Routing Updates

• REQ-ROUTE-001: When auto_merge is "true" and queue_available is "false", both implementation.yaml and remediation.yaml must route to a direct-merge step instead of skipping to cleanup/release.
• REQ-ROUTE-002: The direct-merge step must invoke gh pr merge --squash --auto to enable GitHub-native auto-merge regardless of merge queue presence.
• REQ-ROUTE-003: The direct-merge path must poll PR state for merged completion rather than calling wait_for_merge_queue.

FAIL — Failure Handling

• REQ-FAIL-001: The direct-merge path must handle merge failures (e.g., conflicts from concurrent merges) with a resolve-and-retry pattern analogous to the queue ejection path.
• REQ-FAIL-002: If the direct merge fails due to a non-conflict error, the recipe must route to the same cleanup/release path used by the queue timeout case.

DESC — Ingredient Description

• REQ-DESC-001: The auto_merge ingredient description in both implementation.yaml and remediation.yaml must be updated to reflect that it controls automatic merging after checks pass, not specifically merge queue enrollment.