fix(files): trim message file ids

[aiirvizionz]

Summary

• trim message file route params before validation and lookup
• reject whitespace-only message ids before authentication or database work
• add focused route coverage for trimmed and blank message ids

Tests

• node node_modules\vitest\vitest.mjs run --config $env:TEMP\qryptchat-vitest-minimal.config.mjs "src/app/api/files/message/[messageId]/route.test.js"
• git diff --check

Note: I used the minimal Vitest config already present locally because the repo's default Vitest setup imports @vitejs/plugin-react, which currently fails against the installed Vite package export map in this checkout.