fix(crypto): reject blank public key user ids

[aiirvizionz]

Summary

• Normalize the public-key user_id query parameter before validation.
• Return the existing missing-parameter 400 response for whitespace-only ids instead of doing a target lookup.
• Add regression coverage to ensure blank ids do not call the public-key RPC.

Validation

• git diff --check
• node node_modules\vitest\vitest.mjs run --config %TEMP%\qryptchat-vitest-minimal.config.mjs "src/app/api/crypto/public-keys/route.test.js" (2 tests passed)

I used the same temporary minimal Vitest config needed locally because the repo's default Vitest config currently fails to load through the installed Vite/plugin combination; no dependency files were modified.