Add persistent context files and cleanup stale references

- Add CONTEXT.md: Full infrastructure documentation with architecture diagram,
  routing table, network details, common operations, and important limitations
- Add CLAUDE.md: Project-level context for AI agents working in this codebase
- Add global-claude-md/CLAUDE.md: User-level global context for ~/.claude/
- Delete nginx-ai-proxy.conf: Unused, Caddy replaced nginx on big-server
- Update deploy.sh: Remove stale nginx setup step, update domain to ai.ein-softworks.com
- Update README.md: Remove nginx-ai-proxy.conf from files list, update domain,
  and remove leaked auth token from example

Context files provide persistent reference for AI coding sessions across
all projects and the ein-ai-proxy codebase specifically.

CLAUDE.md

@@ -0,0 +1,22 @@
+# Ein AI Proxy - Project Context
+
+Anthropic-compatible proxy that routes AI requests to multiple providers based on model name: sonnet→GLM-4.7 (Z.ai), opus→Anthropic, haiku→DeepSeek.
+
+## File Structure
+- `proxy.mjs` - Main proxy server (zero dependencies, Node.js built-ins only)
+- `config.json` - API keys and auth token (gitignored)
+- `config.example.json` - Template config
+- `ein-ai-proxy.service` - Systemd unit file
+- `deploy.sh` - Deployment and testing script
+
+## Development
+Run locally: `node proxy.mjs` (requires `config.json`)
+Test health endpoint: `curl http://localhost:3100/health`
+Zero npm dependencies — do not add any.
+
+## Deployment
+On mini-server (ssh mini-server): `cd ~/ai-proxy && git pull && sudo systemctl restart ein-ai-proxy`
+View logs: `sudo journalctl -u ein-ai-proxy -f`
+
+## See Also
+`CONTEXT.md` - Full infrastructure details (network, servers, Caddy, routing table)