Fix completions capability naming to match MCP SDK

[krzysztofwos]

Summary

• Renames the completion capability key to completions (plural) in both the proxy server and child client capability declarations in src/mcp-proxy.ts
• This aligns with the @modelcontextprotocol/sdk >=1.25.x which validates against completions when registering the CompleteRequestSchema handler

Problem

reloaderoo fails to start with:

Error: Server does not support completions (required for completion/complete)

The SDK's assertRequestHandlerCapability checks this._capabilities.completions but the proxy declared completion (singular), so the check always fails.

Test plan

• All existing tests pass (121 unit + 19 integration + 11 e2e)
• Verified end-to-end with a Rust MCP server (rmcp) in Cursor — proxy starts, restart_server tool works, child server restarts successfully

Fixes #9
Fixes #8

[coderabbitai]

Walkthrough

This change updates the MCP completion capability schema declarations in the proxy implementation. The MCPProxy constructor's server capabilities field is renamed from completion to completions with the schema changed from { argument: true } to {}. Similarly, the child Client capabilities field is updated from completion: {} to completions: {}. These changes affect only the capability advertisements and do not modify any request-handler wiring or control flow logic.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and directly summarizes the main change: renaming the completion capability to match MCP SDK requirements.
Linked Issues check	✅ Passed	The pull request fully addresses the linked issue #9 by renaming completion to completions in both server and client capability declarations, resolving the SDK validation failure.
Out of Scope Changes check	✅ Passed	All changes are scoped to the specific issue: only the capability key names were modified in mcp-proxy.ts with no extraneous alterations.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description check	✅ Passed	The pull request description clearly relates to the changeset, explaining the capability key rename from 'completion' to 'completions' and why this fix is necessary.

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