fix(chat): trim participant conversation ids

[aiirvizionz]

Summary

• trim the async conversation ID before participant queries
• reject whitespace-only route parameters with the existing 400 response
• add focused regression coverage

Verification

• node node_modules\vitest\vitest.mjs run --config %TEMP%\qryptchat-vitest-minimal.config.mjs src/app/api/chat/conversations/[id]/participants/route.test.js
• git diff --check

This is a focused hardening fix for the accepted uGig QryptChat testing gig.