Implement streaming decode support in live ONNX/Vitis inference

[Shreyas582]

Scope

Add token streaming decode output path for live ONNX/Vitis inference so operators can observe progress before full completion.

Acceptance Criteria

• Live runtime supports incremental token decode/emit mode.
• JSON output remains contract-compatible when streaming is enabled/disabled.
• Fallback behavior remains deterministic with --live-fallback-policy dry-run-on-error.
• Integration tests cover at least one successful streaming live path.
• Docs updated (README + docs/live-mode-operations.md + docs/upgrades.md + CHANGELOG.md).