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.

global-claude-md/CLAUDE.md

@@ -0,0 +1,4 @@
+AI Proxy: https://ai.ein-softworks.com | Routes: sonnet→GLM-4.7, opus→Anthropic, haiku→DeepSeek
+SSH: big-server (ssh.ein-softworks.com:30141), mini-server (ssh.maybe.zone:41922) via ~/.ssh/id_personal
+Gitea: https://git.ein-softworks.com | mini-server: Debian/zsh, Node v24 via nvm (source before use)
+WARNING: /clear before switching providers mid-conversation when thinking enabled (GLM-4.7 thinking blocks incompatible with Anthropic API)