V9 architecture refactor: restore CI gates and unify execution core

[coeasy]

Scope

• Restore the real Phase 0 CI/build gates without weakening test, security, risk, or capability checks.
• Fix frontend Node 20 compatibility and backend baseline failures.
• Begin V9 Phase 2 with latest-N local bars, explicit source capability errors, exchange-calendar coverage declarations, and persisted bar provenance.
• Begin V9 Phase 3 with a unified ExecutionService for REST/MCP/batch/rebalance/signal order and cancel paths; market-order risk uses a real quote and rejects when unavailable.

Compatibility preserved

FastMCP Streamable HTTP, REST /api/v1/*, WebSocket fan-out, multi-broker/multi-account grid, batch order/cancel/reconnect, and research/paper/WAL/audit/reconcile paths remain in scope and are covered by existing gates.

Verification

• Ruff: passing locally
• Backend targeted and full per-file baseline regression: passing locally
• Frontend lint, Vitest, Vite build: passing locally
• Reconcile, license, capability-drift, and frontend class-name gates: passing locally

This PR intentionally remains open while the remaining V9 phases and same-SHA CI/Windows client build verification are completed. Do not merge automatically.