fix(cron): add spend-neutral provider reset backoff

[jayleaton]

Summary

• parse provider reset hints and persist deterministic bounded backoff after HTTP 429 failures
• suppress unattended fires until backoff expiry while preserving durable failure state and automatic resume
• keep explicit manual runs safe with a dedicated atomic backoff override, including dashboard, background, legacy-provider, and concurrent-pause paths
• make Chronos arm and reconcile one-shots at the effective backoff expiry

Test plan

• HERMES_TEST_FILE_RETRIES=0 scripts/run_tests.sh tests/cron/test_provider_rate_limit_backoff.py tests/cron/test_scheduler_provider.py tests/plugins/test_chronos_cron.py tests/tools/test_cronjob_run_immediate.py tests/tools/test_cronjob_run_background.py tests/cron/test_ticker_stall_60703.py tests/hermes_cli/test_web_server_cron_profiles.py -q (142 passed)
• python -m compileall -q cron/jobs.py cron/rate_limit_backoff.py cron/scheduler.py cron/scheduler_provider.py hermes_cli/web_server.py plugins/cron_providers/chronos/__init__.py tools/cronjob_tools.py
• git diff --cached --check

Operational notes

• Live job dabcf70cf427 (eng-completion) remains active on its unchanged every 10m schedule.
• Durable history confirms recovery after the task's original terminal 429 (2336eaa607544e3ba33fae88e5b76def failed, followed by 29282100a7c549b7b7464c73ad794f81 completed).
• Its latest provider reset is still in the future; the candidate parses the live error to a bounded reset time, while persistence/restart/automatic-resume behavior is covered deterministically in tests.
• No model, provider, reasoning, or X-job configuration was changed.

Do not merge from this task; review only.

[jayleaton]

@Teknium Ready for review. Exact candidate f40e397 is deployed to the live default gateway; the active eng-completion job suppressed its otherwise-due unattended fire during the persisted provider reset window without changing cadence/model/provider, and all 142 focused tests pass. Please do not merge until review is complete.