fix: remove server.url/host/port consistency validator

[evagundan]

Summary

• Remove _validate_server_url_host_port model validator from MilocoSettings

Motivation

The validator assumes server.url matches server.host:server.port, which breaks deployments where the external URL differs from the local bind address:

• Reverse proxy: server.url points to the public URL (e.g. https://miloco.example.com) while server.host is 127.0.0.1
• Hermes platform: server.url may point to a different host/port for agent webhook callbacks
• Docker/WSL: Network address translation means the external URL differs from the internal bind address

The validator only emits a warning (doesn't block startup), but the warning is misleading in these scenarios — the configuration is intentional, not a mistake.

Changes

• backend/miloco/src/miloco/config/settings.py: Remove _validate_server_url_host_port method and its comment block (49 lines removed)

Testing

• Verified the app starts correctly with mismatched server.url and server.host:server.port
• No other code depends on this validator

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions]

👋 感谢提交 PR @evagundan！维护者会尽快 review。

提交前请确认：

• CI 全绿（test / lint / build）
• 改动聚焦单一主题，便于审阅
• 若改动了依赖（lockfile / pyproject.toml / package.json），需维护者评论 /allow-dependencies-change <当前 head SHA> 放行（之后再 push 需重新放行）