fix(chat): reject blank mark-read conversation ids

[aiirvizionz]

Summary

• Normalize the mark-read conversation id before validation and message filtering.
• Reject missing or whitespace-only ids before creating the Supabase server client.
• Add regression coverage for blank route params so invalid requests do not do auth/database work.

Validation

• git diff --check
• node node_modules\vitest\vitest.mjs run --config %TEMP%\qryptchat-vitest-minimal.config.mjs "src/app/api/chat/conversations/[id]/mark-read/route.test.js" (3 tests passed)

I also attempted direct execution with the repo's default Vitest config, but the local config currently fails to load because @vitejs/plugin-react imports vite/internal, which is not exported by the installed Vite package. I used a temporary minimal Vitest config only to run this route test and did not modify dependency files.