feat: execute reviewed derivative spreads

[felipecsl]

Context

Issue #49 completes the epic by allowing only an exact, previously reviewed preview to become one guarded atomic vertical, then verifying warning and order lifecycle state through terminal outcomes.

What changed

• persists short-lived previews and guarded execution expectations with owner-only files, account digests, and masked DTOs—never full account IDs
• adds spread submit, explicit warning acknowledgment, and order show|watch|cancel
• revalidates account/session/environment, preview expiry, contract identity, ratios, quantity, limit, TIF, and session before submission
• generates unique client order IDs and verifies returned legs/economics after placement
• stops on unknown warnings and requires exact explicit confirmation for known reply IDs
• exposes partial/full/rejected/canceled/warning-pending lifecycle state and verifies cancellation reaches CANCELED
• requires live opt-in plus an exact account allowlist; paper remains the safe default
• adds all seven guarded derivative MCP tools over the same research, preview, and execution services
• retains the existing Schwab single-leg MCP behavior
• consumes @huskly/ibkr-client@^0.11.0

Validation

• yarn run check
• yarn build
• 12 test files passed
• built MCP server starts and exits cleanly over stdio

Closes #49