Add frontend environment configuration for API URL injection

- .env.example: Documentation template
- .env.development: Local dev defaults (localhost:5000)
- .env.production: Production defaults (relative /graphql path)
- Updated .gitignore to track non-secret env files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -169,9 +169,11 @@ $RECYCLE.BIN/
 # Environment & Secrets
 # ============================================
 .env
-.env.*
+.env.local
+.env.*.local
 !.env.example
-!.env.*.example
+!.env.development
+!.env.production
 *.pem
 *.key
 *.p12