fix: Resolve socket mixed content error by making the socket connection URL environment-aware for production and development, and adding Vite client type definitions.

docs/development/devlog/2025-12-16-183000_fix_socket_mixed_content.md

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+# Fix Socket Mixed Content Error
+
+## Objective
+Resolve the "Mixed Content" error preventing the Online Lobby and Deck Tester from functioning in the production Kubernetes environment. The application was attempting to connect to an insecure HTTP endpoint (`http://...:3000`) from a secure HTTPS page.
+
+## Changes
+- **Client Socket Service**: Modified `client/src/services/SocketService.ts` to make the connection URL environment-aware.
+    - In **Production**: The URL is now `undefined`, allowing Socket.IO to automatically detect the current protocol (HTTPS) and domain (via Ingress), avoiding mixed content blocks.
+    - In **Development**: It retains the explicit `http://localhost:3000` (or hostname) to ensure connectivity during local development.
+- **TypeScript Config**: Added a reference directive `/// <reference types="vite/client" />` to `SocketService.ts` to ensure `import.meta.env` is correctly typed during the build.
+
+## Verification
+- Validated that `npm run build` succeeds without TypeScript errors.
+- Confirmed that the fix aligns with standard Vite + Socket.IO production deployment patterns.