feat(flow): add Flow DSL v1 runtime, CLI, docs, and coverage

[huhuanming]

Summary

• add Flow DSL v1 core runtime in ScriptoriaCore/Flow (validate/compile/run/dry-run support)
• add CLI entrypoints for scriptoria flow (validate, compile, run, dry-run)
• integrate flow execution with script runner / post-script agent path and provider executable selection
• add end-to-end and boundary test coverage for flow engine, CLI behavior, provider adapters, and gate parsing
• add flow docs, migration notes, examples, and TC mapping generation script

Testing

• swift test (169 passed)