fix(cron): classify no-agent failures as script errors

[visualfox-ch]

Summary

• classify no_agent=True cron failures before provider/API heuristics
• keep timeout, rate-limit, and auth-like script output source-accurate
• add regression coverage proving script-only failures never claim a provider fallback

Problem

A script-only watchdog timeout was delivered as provider timeout with Fallback chain was exhausted, even though no_agent=True skips the LLM and provider path entirely.

Verification

• python -m pytest tests/cron/test_cron_no_agent.py -q -o addopts= — 21 passed
• python -m ruff check cron/scheduler.py tests/cron/test_cron_no_agent.py — passed
• git diff --check — passed

Assisted-by: Hermes:gpt-5.6-sol

[visualfox-ch]

Superseded by #64474, which carries the same focused no-agent cron failure classification on current main with the targeted test suite passing.