fix: honor derived runtime continuity before HTTP execution

[Pigbibi]

Summary

• Consume the existing derived runtime_target_enabled setting before market-hours evaluation and the strategy cycle.
• Preserve the explicit HTTP and environment switches; RECONCILE_ONLY and PAUSED cannot enter the ordinary execution path.
• Add the 10-case continuity matrix with synthetic runtime settings and broker-construction failure assertions. No new contract, gate, dependency, workflow, or runtime configuration.

Verification

• Baseline main in memory: continuity regression 2 failed / 8 passed, precisely RECONCILE_ONLY and PAUSED with enabled=true.
• Candidate plus unchanged baseline accounting module: request-handling and runtime-config tests 68 passed.
• Full local working-tree focused regression: request-handling, runtime-config, and reconciliation tests 127 passed. Separate unfinished accounting edits are NOT in this PR.
• All local pytest runs used deny-network sandbox and temporary cloud-loader stubs; no real broker/provider/cloud call.
• ruff check main.py tests/test_request_handling.py and git diff --check passed.

Safety / scope

• Only main.py and tests/test_request_handling.py are committed.
• Deploy Cloud Run is workflow_dispatch-only; this PR does not dispatch deploy/config/Scheduler/IAM or runtime workflows.
• No actual /run, /probe, broker login/refresh, order, or account operation performed. Synthetic tests are not production recovery evidence.