fix(diagnose): read cron failures from nested state

[szafranski]

Summary

• read cron run status and errors from the nested state object
• update diagnose E2E fixtures to match the CronJobResponse contract
• cover both diagnose cron summary and diagnose overview

Root cause

The diagnose commands read last_status and last_error from the job's top level, while the API serializes those fields under state. The existing test fixture used the same incorrect flat shape, so it did not catch the mismatch.

Validation

• cargo test -p aionui-app --test diagnose_cli_e2e
• cargo clippy -p aionui-app -- -D warnings
• cargo fmt --all -- --check
• just push - 8,188 passed, 24 skipped

Existing diagnose output is sufficient; no logging changes are needed.

Fixes #665