Stage O-B: Hera drains her own mail at the idle point, not on the ~1 s idle beat (FABRIC-3.9.0 §2.5)

- sk_vm_idle_point(may_drain_self): with no frame live and mail pending,
  Hera drains one message and returns to the poll loop. Readline passes
  n == 0 (the mid-edit gate), headless 1, the key read 0.
- Removed sk_repl_idle()'s timer-paced drain of Hera's queue and the two
  flags that guarded it (g_mama_interpreting, g_idle_pump_active) -- the
  idle point's frames check already covers that re-entry hazard.

Probe (reverted), all three ISAs: admission -> drain for mail to an idle
Hera 0-1 beats (was up to 100); a message arriving mid-edit is held until
the line is entered (2080-3587 beats), never printed into typed text; an
event queued during a busy line drains when it ends; BLK-ATTACH at boot 1
beat. Acceptance passes; parity, dict_hash set and relay ledger unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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