Python: Fix AG-UI reasoning role and multimodal media parsing to follow specification (#5389)

* Fix AG-UI reasoning role and multimodal media value field parsing

Fix two spec compliance issues in the AG-UI integration:

1. ReasoningMessageStartEvent now uses role='reasoning' instead of
   role='assistant', matching the AG-UI specification for reasoning
   messages.

2. _parse_multimodal_media_part now reads the 'value' field from source
   dicts (with fallback to 'data' for backward compatibility), matching
   the current AG-UI InputContentSource specification.

Bump ag-ui-protocol dependency from ==0.1.13 to >=0.1.16,<0.2 to pick
up the SDK fix that accepts role='reasoning' in ReasoningMessageStartEvent.

Fix pre-existing pyright reportMissingImports errors for orjson in sample
files, and fix import ordering in foundry-hosted-agents sample.

Fixes #5340

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Python: Fix AG-UI reasoning role and multimodal media parsing to follow specification

Fixes #5340

* Remove unintended .maf-runtime-ready marker file

Address PR review feedback: the .maf-runtime-ready file is not referenced anywhere in the repo and was left over from automation.

Fixes #5340

* Python: Fix duplicate AG-UI multimodal 'value' parsing in snapshot path

The snapshot normalization path used a second copy of the multimodal source
parsing logic that still read the deprecated 'data' field. When clients sent
base64 media with source={"type": "base64", "value": ...}, the snapshot event
emitted by the server dropped the payload, causing AG-UI-compatible clients
to crash on ingest.

Extract the shared source-field extraction into _extract_multimodal_source_fields
so both _parse_multimodal_media_part and the snapshot _legacy_binary_part stay
in sync with the AG-UI spec. Add snapshot-path regression tests covering
value-only, value-preferred-over-data, and the legacy data-field fallback.

Addresses review feedback on #5389 from @Rickyneer.

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/ag-ui/pyproject.toml

@@ -23,7 +23,7 @@ classifiers = [
 ]
 dependencies = [
     "agent-framework-core>=1.1.1,<2",
-    "ag-ui-protocol==0.1.13",
+    "ag-ui-protocol>=0.1.16,<0.2",
     "fastapi>=0.115.0,<0.133.1",
     "uvicorn[standard]>=0.30.0,<0.42.0"
 ]