feat(config): add GOCLAW_CRON_JOB_TIMEOUT env var override

[nguyennguyenit]

Summary

• Add GOCLAW_CRON_JOB_TIMEOUT env var to override cron.job_timeout from config file.
• Aligns with existing GOCLAW_* env var convention.

Closes #1098.

Test plan

• go build ./...
• go test ./internal/config/...
• Verify GOCLAW_CRON_JOB_TIMEOUT=1h ./goclaw overrides default 10m at runtime.

[mrgoonie]

Backlog triage note: this is the cleaner merge candidate for GOCLAW_CRON_JOB_TIMEOUT / #1098, but #1099 contains useful env override tests that this PR does not include. Recommended next step before merge: add equivalent tests here or explicitly decide the duplicate test coverage is not needed, then #1099 can be closed.

[mrgoonie]

Cron-safe maintainer check: this is a tiny, clean implementation for #1098 and CI is green, but I am not merging it yet because duplicate PR #1099 already carries useful internal/config/config_load_test.go coverage for the same env override.nnDecision: defer / needs consolidationnEvidence:n- This PR only adds envStr("GOCLAW_CRON_JOB_TIMEOUT", &c.Cron.JobTimeout) in internal/config/config_load.go.n- #1099 implements the same override and adds targeted tests for env override, invalid fallback, unset default, and env-over-file precedence.n- CronConfig.JobTimeoutDuration() already has duration/default/invalid parsing tests, but this PR does not directly test the env mapping path.nnNext step: please port the relevant config-load env override tests from #1099 into this cleaner PR, then #1099 can be closed as duplicate and this PR should be mergeable if CI stays green.

[mrgoonie]

Summary: This is the right underlying config change, but this PR should not be the merge target as-is because it duplicates the older, more complete PR #1099 for the same issue #1098.

Risk level: Low

Mandatory gates:

• Duplicate/prior implementation: duplicate found — #1099 already implements GOCLAW_CRON_JOB_TIMEOUT for #1098 and includes focused config-load tests.
• Project standards: issue found — this PR adds the env mapping but no regression test for env override precedence or duration fallback behavior.
• Strategic necessity: clear value, but should be consolidated into one PR.
• CI/checks: green

Findings:

• Important: Please coordinate with #1099 or close this PR in favor of it. #1099 covers the same env var mapping and also adds tests for env override, invalid duration fallback, unset default, and env-over-file precedence. Keeping two open PRs for the same one-line config surface creates duplicate review/merge risk.
• Important: If this PR remains the chosen successor, add equivalent tests in internal/config/config_load_test.go before re-review.

Verdict: REQUEST_CHANGES

Next step: either close this PR in favor of #1099, or explicitly supersede #1099 and bring over the regression tests.