fix: flush large piped tool output

[haosenwang1018]

Summary

• replace console.log() in call output with an explicit stdout writer
• wait for drain when stdout backpressure is applied
• preserve the existing CLI-friendly text output format

Problem

Issue #23 reports that large tool results are truncated at 65536 bytes when mcp-cli call ... is piped to another process. This points to the output path not respecting pipe backpressure.

Fix

The call command now writes formatted tool output through process.stdout.write() and awaits the drain event when needed, instead of relying on console.log(). That keeps the same output shape while ensuring large responses are fully flushed through piped stdout.

Fixes #23

Validation

• git diff --check
• npx tsc --noEmit
• bun test tests/config.test.ts
• bun test tests/output.test.ts
• npx @biomejs/biome check src/commands/call.ts