feat: serve llms.txt from self-hosted dashboard

[mtalhazulf]

Add llms.txt to the self-hosted Dokploy app's public directory so every instance serves it at /llms.txt for AI tool discoverability, pointing to the documentation index at docs.dokploy.com/llms.txt.

What is this PR about?

Please describe in a short paragraph what this PR is about.

Checklist

Before submitting this PR, please make sure that:

• You created a dedicated branch based on the canary branch.
• You have read the suggestions in the CONTRIBUTING.md file https://github.com/Dokploy/dokploy/blob/canary/CONTRIBUTING.md#pull-request
• You have tested this PR in your local instance. If you have not tested it yet, please do so before submitting. This helps avoid wasting maintainers' time reviewing code that has not been verified by you.

Issues related (if applicable)

closes #4480

Screenshots (if applicable)