Remove duplicate tool call parsing in OpenResponses provider

[Kamilbenkirane]

Priority: Critical
Related: #199

modalities/text/providers/openresponses/client.py:142-154 re-implements tool call parsing inline instead of calling parse_tool_calls() from the protocol module. Same duplication in streaming at lines 53-69. This defeats the purpose of the protocol base class.

What to fix:

• Replace inline parsing in _parse_tool_calls() with call to parse_tool_calls() from celeste.protocols.openresponses.tools
• Replace inline streaming aggregation with delegation to protocol function
• Verify behavior is identical after refactor

Files:

• src/celeste/modalities/text/providers/openresponses/client.py:53-69, 142-154
• src/celeste/protocols/openresponses/tools.py:56-77

[Kamilbenkirane]

Resolved by #229 — the provider-level OpenResponses text client was removed entirely. Parsing now lives only in the protocol layer.