fix(jobs): block create only on live duplicate id (#11)

[mattmezza]

Problem

Agent job creation was sometimes refused with "Request already fulfilled; not repeating write actions" — even for a brand-new job id (e.g. flight-monitor-lx1272). The job was never created, so recurring/one-shot monitors could not be scheduled reliably.

Root cause

Two issues, both off the job id:

1. core/agent._execute_tool ran every write through a per-turn dedup guard keyed on tool + params. A manage_jobs create that ran earlier in the same turn blocked any later create, regardless of id.
2. _tool_manage_jobs create never checked id existence at all — it silently upserted over a live job; there was no correct id-based guard to take the generic one's place.
3. tools/jobs.py CLI blocked recreation of any existing id, including done/cancelled ones.

Fix

Match the issue's expected behavior exactly — block a create only when a job with the same id already exists and is active/paused:

• Exempt manage_jobs from the generic per-turn write-dedup guard.
• Guard _tool_manage_jobs create on job_id + status: explicit live id → blocked with an id-based message; done/cancelled ids and auto-generated ids are free to (re)create.
• Same active/paused-only rule in the jobs.py CLI.

Tests

tests/test_tools.py:

• brand-new id creates even after another job was made the same turn (the repro);
• recreating a live id is blocked with an id-based message, not the generic guard;
• a cancelled id can be recreated;
• the generic dedup guard still suppresses an identical repeated send_email.

Full suite: 326 passed.

Closes #11