fix(cli): detect GraphQL files in run attachments

[ChuanWeis]

Summary

• map .graphql and .gql run attachments to application/graphql
• add coverage for both extensions in the run-command MIME tests

Addresses PlatformNetwork/bounty-challenge#53309.

Verification

• git diff --check
• cargo test -p cortex-cli mime_type_from_extension could not be run locally because cargo is not installed/exposed on this machine.

[greptile-apps]

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[ChuanWeis]

Update: I installed the Rust toolchain locally and reran validation for this branch.

• cargo check -p cortex-cli passes.
• cargo test -p cortex-cli mime_type_from_extension currently fails before reaching the MIME test because the upstream test module src/cortex-cli/src/agent_cmd/tests.rs imports private read_file_with_encoding. That compile error appears unrelated to this GraphQL MIME mapping change.