fix: log MCP client close errors instead of silently swallowing them

[dhruv1220]

Closes #145.

What changed

client.close() failures in the MCP session helper (src/server/connections.ts) and the Parallel web-search transport (src/server/parallel.ts) were swallowed with an empty .catch(() => {}). They now log the failure reason through console.error, matching the existing server-side diagnostic convention (see setup-telemetry.ts).

Why

Swallowed close errors masked transport leaks and connection errors in production — operators had zero visibility into why MCP connections accumulated or refused to close cleanly.

Testing

• New regression test in tests/parallel.test.ts: a rejecting client.close() surfaces the reason via console.error while the successful result still returns (red-checked: fails on unpatched code).
• tests/parallel.test.ts + tests/workspace.test.ts: 13/13 green.
• Full suite: 343 passed; the only 2 failures are the pre-existing network-dependent tests/transport.test.ts cases, which fail identically on clean main.
• tsc --noEmit, eslint, prettier --check clean; production build (npm run build) green.