feat: autonomous global opportunity hunter

[moelayyan90]

Adds a global back-to-back opportunity hunter to XGuard mainnet with strict Shariah filtering, pre-funded buyer gating, landed-cost economics, fraud/sanctions/inventory risk gates, D1 persistence, signed ingestion, idempotent execution submission, scheduled operation, conservative shadow defaults, and focused tests.

Safety invariants:

• prohibited or Shariah-ambiguous categories never become executable
• buyer funds must be secured and available before supplier purchase
• supplier inventory and identities must be verified
• net profit is calculated after shipping, duties, platform/payment/FX/other costs
• live execution is disabled unless an HTTPS execution connector and encrypted secret are configured
• execution requests are signed and idempotent