[codex] add input length guards

[saurabhhhcodes]

What changed

• Added backend validation for chat messages so empty or oversized messages are rejected before save.
• Added backend validation for server names so create-server requests are normalized and capped.
• Added frontend length caps and live counters for the chat composer and server name input.

Why

The app was accepting free-form input without clear length guardrails. That created a mismatch between the UI and server expectations and left room for invalid payloads.

Impact

Users now get immediate feedback in the UI, and the backend rejects invalid requests consistently.

Validation

• git diff --check
• node --check server/src/routes/chat.js
• node --check server/src/routes/servers.js
• npm run build in frontend

Closes #135

[vercel]

Someone is attempting to deploy a commit to the Sunil Kumar's projects Team on Vercel.

A member of the Team first needs to authorize it.

[saurabhhhcodes]

Closing this as a duplicate of the already-open input-limit PR #183 so we avoid overlapping work.