Add trigger-run Dataset Deal alternative

[longquanzheng]

Summary

• model each Dataset Deal start or condition submission as a short Dex trigger Run under one execution FlowID
• persist immutable process snapshots and all execution state in PostgreSQL with optimistic version checks and indexed filters
• commit one action per step using RunID plus StepExecutionID for idempotency, and return 409 for conflicting triggers
• update the REST API, seller/buyer UI, demo scripts, and documentation for PROCESSING, WAITING, and COMPLETED execution state

Tests

• make -C examples/go unitTests
• make -C examples/go e2eTests
• make -C examples/go datasetDealDemo (isolated ports)
• make copyright-check