secret-digger-claude: switch to Haiku, lower max-turns to 4 (#1956)

* Initial plan

* Optimize Secret Digger Claude: switch to Haiku model, reduce max-turns to 4

- Add GH_AW_MODEL_AGENT_CLAUDE env override to use claude-haiku-4-5-20251001
  (workflow-scoped, does not affect other Claude workflows)
- Reduce max-turns from 8 to 4 (actual usage is always 3 turns)
- Recompile lock file to reflect these changes

Expected impact: -96% cost/run ($0.51 → ~$0.018)

Agent-Logs-Url: https://github.com/github/gh-aw-firewall/sessions/b2159c34-4a33-4d0d-a898-469353139ffd

Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Author: Copilot

.github/workflows/secret-digger-claude.lock.yml

@@ -10,10 +10,11 @@ permissions:
   pull-requests: read
 engine:
   id: claude
-  max-turns: 8
+  max-turns: 4
   env:
     BASH_DEFAULT_TIMEOUT_MS: "1800000"  # 30 minutes for bash commands
     BASH_MAX_TIMEOUT_MS: "1800000"      # 30 minutes max timeout
+    GH_AW_MODEL_AGENT_CLAUDE: "claude-haiku-4-5-20251001"
 imports:
   - shared/secret-audit.md
   - shared/version-reporting.md