fix(chat): resolve async mark-read route params

[rissrice2105-agent]

Summary

• Resolve async Next.js route params before reading the conversation id in the mark-read API
• Return a 400 response when the route id is missing instead of continuing with an undefined conversation filter
• Add regression coverage for Promise-based params

Tests

• corepack pnpm exec vitest run --config $env:TEMP/qryptchat-vitest-no-react.config.mjs "src/app/api/chat/conversations/[id]/mark-read/route.test.js"
• corepack pnpm exec oxlint "src/app/api/chat/conversations/[id]/mark-read/route.js" "src/app/api/chat/conversations/[id]/mark-read/route.test.js"

Note: the default vitest.config.js currently fails to load locally because @vitejs/plugin-react imports a non-exported Vite internal path, so the focused test was run with a minimal no-React Vitest config.