feat(core): repair malformed llm grader output

[christso]

Closes #911

Summary

• add a final structure-repair retry for llm-grader after the 3 standard attempts fail on malformed structured output
• reuse the last invalid grader response plus validation error instead of re-grading from scratch
• skip the repair path when the grader returned no content to salvage
• document the AgentV OSS board claim workflow fix in AGENTS.md so missing project items are added before status updates

Verification

• bun test packages/core/test/evaluation/evaluators.test.ts packages/core/test/evaluation/evaluators_variables.test.ts packages/core/test/evaluation/orchestrator.test.ts
• pre-push hook passed: build, typecheck, lint, test, validate eval YAML files

Red/Green UAT

Red on main:

• bun apps/cli/src/cli.ts eval /tmp/agentv-911-redgreen/repair.eval.yaml --target candidate_mock --output /tmp/agentv-911-redgreen/main.red.jsonl
• result: repair-check was skipped with Grader parse failure after 3 attempts, and /tmp/agentv-911-redgreen/main.red.jsonl recorded execution_status: execution_error with score: 0

Green on this branch:

• bun apps/cli/dist/cli.js eval /tmp/agentv-911-redgreen/repair.eval.yaml --target candidate_mock --output /tmp/agentv-911-redgreen/branch.green.jsonl
• result: the same eval passed with score: 1 after the grader script received the structure-repair prompt, and /tmp/agentv-911-redgreen/branch.green.jsonl recorded execution_status: ok

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