feat(honcho): dialectic liveness — stale-thread watchdog, stale-result discard, empty-streak backoff

Hardens the dialectic lifecycle against three failure modes that could
leave the prefetch pipeline stuck or injecting stale content:

- Stale-thread watchdog: _thread_is_live() treats any prefetch thread
  older than timeout × 2.0 as dead. A hung Honcho call can no longer
  block subsequent fires indefinitely.

- Stale-result discard: pending _prefetch_result is tagged with its
  fire turn. prefetch() discards the result if more than cadence × 2
  turns passed before a consumer read it (e.g. a run of trivial-prompt
  turns between fire and read).

- Empty-streak backoff: consecutive empty dialectic returns widen the
  effective cadence (dialectic_cadence + streak, capped at cadence × 8).
  A healthy fire resets the streak. Prevents the plugin from hammering
  the backend every turn when the peer graph is cold.

- liveness_snapshot() on the provider exposes current turn, last fire,
  pending fire-at, empty streak, effective cadence, and thread status
  for in-process diagnostics.

- system_prompt_block: nudge the model that honcho_reasoning accepts
  reasoning_level minimal/low/medium/high/max per call.

- hermes honcho status: surface base reasoning level, cap, and heuristic
  toggle so config drift is visible at a glance.

Tests: 550 passed.
- TestDialecticLiveness (8 tests): stale-thread recovery, stale-result
  discard, fresh-result retention, backoff widening, backoff ceiling,
  streak reset on success, streak increment on empty, snapshot shape.
- Existing TestDialecticCadenceAdvancesOnSuccess::test_in_flight_thread_is_not_stacked
  updated to set _prefetch_thread_started_at so it tests the
  fresh-thread-blocks branch (stale path covered separately).
- test_cli TestCmdStatus fake updated with the new config attrs surfaced
  in the status block.

tests/honcho_plugin/test_cli.py

@@ -26,6 +26,9 @@ class TestCmdStatus:
             write_frequency = "async"
             session_strategy = "per-session"
             context_tokens = 800
+            dialectic_reasoning_level = "low"
+            reasoning_level_cap = "high"
+            reasoning_heuristic = True
 
             def resolve_session_name(self):
                 return "hermes"