fix(cortex_agent): fix SSE response parsing for Cortex Agent API

[shibinmatrix]

Summary

• Remove stream: False from the Cortex Agent request payload. This parameter caused Snowflake to return plain JSON instead of SSE, but parse_agent_response() expects SSE format with event: response markers. Without streaming, the parser found zero events and always returned "No final response found.".
• Fix content[-1] assumption in parse_agent_response(). The response content array contains multiple types (thinking, tool_use, tool_result, text, suggested_queries). The last item is suggested_queries, not text. The fix iterates the array and explicitly finds the item with type == "text".

Root Cause

The cortex_agent tool always returned {"results": "No final response found."} due to two compounding bugs:

1. tools.py:79 — "stream": False was included with the comment "Ignored by Agent API", but it is not ignored. Snowflake returns Content-Type: application/json (a single JSON blob) instead of text/event-stream (SSE). The parser then iterates over JSON lines looking for event: response and never finds it.

2. utils.py:312-316 — Even when streaming works correctly, content[-1].get("text") grabs the wrong item. The suggested_queries content type appears after text in the array, so the last element has no text field and falls back to the default "No final response found.".

Test plan

• Verified standalone REST call to Cortex Agent with streaming enabled returns valid SSE with event: response
• Verified the event: response data payload contains a content array where the text item is NOT the last element
• Verified the fix end-to-end: cortex_agent MCP tool now returns actual agent responses
• Verified requests appear in Snowflake Cortex Agent Activity monitoring page