fix(kanban): teach workers valid foreground terminal calls

[brownser]

Observed Banger Ledger coder and raven worker sessions repeatedly send heartbeat=60 with foreground terminal calls; terminal correctly rejects this background-only argument, and runs timed out without accepted artifacts. Add worker-only guidance to omit notify/heartbeat on foreground calls, correct invalid arguments once, and never reroute a security denial. Regression covers prompt guidance and handler contract. Tests: 55 passed, 2 skipped (prompt builder + process heartbeat). No runtime activation or review verdict claimed. Rollback: revert 162e464.

[kvnloo]

Independent exact-head check on 162e464893aafac3adaa8cc3e41e2b105f77529b: I mirrored this patch in kvnloo#198 and ran the kanban worker prompt regression.

• focused patched case: 1 passed
• full test_prompt_builder.py: 55 passed
• negative control: 1 failed
• restored: focused case + full file green

This confirms the worker guidance now distinguishes foreground terminal calls from background=true calls that may use notify / heartbeat.

[teknium1]

Heads-up: #133793 lands this class at the dispatcher instead — a foreground terminal call that carries a positive heartbeat runs once with the heartbeat dropped (cherry-pick of #119201 with authorship kept, plus the test/schema follow-up), while a foreground notify=true stays refused. Live repro in that PR body uses the exact argument shapes recorded from 173 production refusals this week. If it merges, this PR becomes unnecessary and will be closed as superseded with credit; leaving it open until then.

[teknium1]

Superseded by #133793 (landed as cb6ffe6): a foreground terminal call that carries heartbeat now runs instead of being refused, so kanban workers no longer need a prompt-side workaround. Thanks @brownser for tracking this down.