refactor(b09): drop bound-cycle STRATEGY_RUNTIME module fallback

[Pigbibi]

Summary

B09 PR-3 (after #360): while a RunContext is bound, cycle code must not fall back to module STRATEGY_RUNTIME. Tests poison the module to prove no leakage.

Changes

• resolve_strategy_runtime: bound → require ctx.strategy_runtime (fail-closed if missing); unbound → module/fallback still allowed for patches.
• _activate_execution_strategy_runtime: when bound, mount on context only — does not rewrite module STRATEGY_RUNTIME (pool knobs still refresh).
• Unbound activate still updates module for build_live_runtime / test compat.
• Tests: poison-module isolation, activate-while-bound no module leak, unbound compat preserved.

Explicitly unchanged (B04)

• No runtime_support.py changes (submission / owner / runtime_call_client untouched).
• No LB-HK / Firstrade / QRS Environments / secrets / Cloud Run.
• ContextVar retained (no signature explosion this PR).

Verification

.venv/bin/python -m unittest tests.test_run_context -v
.venv/bin/python -m unittest \
  tests.test_state_service \
  tests.test_trend_pool_loading \
  tests.test_cycle_service \
  tests.test_runtime_support \
  tests.test_cycle_replay_runtime \
  tests.test_strategy_runtime \
  tests.test_notify_i18n \
  -v

Local: 15 + 133 green.

Author: Pigbibi. No CloudAgent.