Basic scaffold and initial 2 tools for x

[pratikbuilds]

Summary

• add getUsersMe and getUsersByUsername
• expose the Interchange sidecar bundle and x-api credential declaration
• add the fetch-based X API client with timeout, cancellation, and error handling
• add local Interchange linking, build configuration, and CI
• add focused client, tool-runner, and sidecar tests

Validation

• bun run typecheck
• bun test --conditions intx-src src
• bun run build
• bun pm pack --dry-run