fix(mcp): disable bun fetch idle timeout for remote transports

[viperx1]

Issue for this PR

Closes #39584

Type of change

• Bug fix

What does this PR do?

mcp.timeout (e.g. 1200000) is passed through to the MCP SDK correctly, but on the Bun runtime a long MCP call that is silent for >300 s dies earlier with "The operation timed out." because Bun's fetch() enforces a default 300 s socket-idle timeout. The MCP timeout ceiling is never reached.

This adds an inline transport-level fetch that passes Bun's non-standard timeout: false to both StreamableHTTPClientTransport and SSEClientTransport, disabling Bun's idle timeout so the MCP SDK request timeout becomes the authoritative ceiling. This mirrors the same timeout: false already used for the provider fetch in provider.ts and the AI SDK fetch in core/src/aisdk.ts.

How did you verify your code works?

• Built the Linux TUI binary and confirmed it compiles and successfully reaches timeouts higher than 300 s.
• The change is additive (a transport fetch wrapper) and reuses an option already used in the provider path.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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