[squad-plan] Tighten Avenger max-turns budget to match documented hard limit

[github-actions]

Objective

Reduce Avenger's max-turns frontmatter budget from 50 to a tighter limit that matches the prompt's own documented turn budget.

Issue context

Issue #50312 found Avenger frontmatter sets max-turns: 50, but the workflow's own "Execution Guidelines" state "Hard limit is 25 turns." The looser config allows expensive outlier runs (the highest-cost audited run also had the highest cache-read volume) and weakens budget enforcement (~3-5% estimated AIC savings on outliers).

Implementation guidance

• Edit .github/workflows/avenger.md.
• Change top-level max-turns from 50 to a tighter value, preferably 25 (matching the documented hard limit) unless a strong implementation reason justifies up to 30.
• Ensure the prompt wording and frontmatter stay consistent — there should be exactly one clear turn-budget story, not two conflicting numbers.
• Run make recompile after editing so the .lock.yml is regenerated.

Acceptance criteria

• Avenger frontmatter max-turns value is aligned with the prompt's documented guidance (no contradiction between the two).
• make recompile succeeds and the generated lock file updates cleanly with no unrelated diffs.

Dependency / ordering notes

Independent quick config/doc change; can be done in parallel with the Step 0 CI re-check fix. Consider bundling both Avenger markdown edits into one PR if per-issue assignment granularity isn't strictly required, since both touch the same file.

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_{Comment /squad-plan to run again}