docs: clarify headers config for streamable-http and sse MCP servers

[jackila]

Description

Clarified mcpServers docs for remote MCP transports by explicitly documenting that custom request headers for sse and streamable-http should be configured under requestOptions.headers in YAML.

Also added a concrete YAML example for a streamable-http server with custom headers to reduce confusion between YAML config and JSON-style MCP configs.

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

N/A (documentation-only change).

Tests

No runtime tests were added (documentation-only change).
I validated the updated docs content and ensured no linter issues were introduced in the edited file.

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Summary by cubic

Clarifies how to configure custom HTTP headers for sse and streamable-http MCP servers by specifying them under requestOptions.headers in YAML. Adds a concise YAML example to avoid confusion with JSON-style configs.

^{Written for commit b1dfdc0. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file

[jackila]

I have read the CLA Document and I hereby sign the CLA

[jackila]

recheck