Add openweb-ui service stack and docs

[wrightwells]

After seeing Alex's youtube about this repo.....

It allows local and tailscle access.

Pull Request Title: Add OpenWebUI service stack with Tailscale + Ollama and setup docs

Description

This pull request adds a new services/openweb-ui stack to run OpenWebUI behind Tailscale, with Ollama as the local model backend.

Purpose

• Provide a ready-to-run Docker Compose deployment for OpenWebUI + Ollama.
• Route service access through Tailscale Serve over HTTPS.
• Document configuration and startup steps clearly.

Background / Details

• Added docker-compose.yml with:
  • tailscale service (network boundary, serve config, healthcheck, tun/net_admin requirements)
  • ollama service (shared network namespace with tailscale, GPU-enabled)
  • open-webui service (shared network namespace, points to local Ollama endpoint)
• Added stack.env.example with safe placeholders for all required environment variables.
• Added README.md explaining architecture, file roles, env setup, startup commands, and operational notes.

Related Issues

• N/A (no linked issue)

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring

How Has This Been Tested?

1. Verified files exist in repo under services/openweb-ui/:
   • docker-compose.yml
   • stack.env.example
   • README.md
2. Verified git commit and push completed successfully to main:
   • Commit: 1f2fd75
   • Push range: 85dfa16..1f2fd75

Checklist

• I have performed a self-review of my code
• I have added tests that prove my fix or feature works
• I have updated necessary documentation (e.g. frontpage README.md)
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A (no UI changes captured in this PR)

Additional Notes

• stack.env is intentionally not committed. Use stack.env.example as template.
• Deploy key push required explicit SSH identity selection during push.

[jackspiering]

Duplicate of #230.