fix: startup banner always shows 127.0.0.1 regardless of server.host

[Sycun]

Summary

Fixes #301

Investigation of the reported issue ("config.yaml 的 host 配置不生效，服务一直绑定在 127.0.0.1"):

The actual listen binding was already correct. With host: 0.0.0.0 the server does listen on all interfaces (lsof shows *:port); with host: 127.0.0.1 it binds loopback only. internal/app/app.go has always used cfg.Server.Host.

The real problem is the startup banner: internal/termout/startup.go hardcoded http://127.0.0.1:<port>/, so no matter what server.host was set to, the first thing the user saw was a 127.0.0.1 URL — which is why the host setting appeared not to take effect while other settings did.

Changes

• StartupWebUIOptions gains a Host field; cmd/server/main.go passes cfg.Server.Host
• New startupHosts(): wildcard binds (0.0.0.0 / :: / empty) expand to 127.0.0.1 plus the machine's non-loopback IPv4 addresses; an explicit host is shown as-is (IPv6 bracketed via net.JoinHostPort)
• Banner now renders, e.g. for 0.0.0.0:

● ONLINE   https://127.0.0.1:8080/
  Network  https://192.168.0.5:8080/
  TLS      self-signed · accept the browser warning once

Test plan

• New unit tests in internal/termout/startup_test.go: explicit host, wildcard expansion (dedup, IPv4-only, loopback first), IPv6 bracketing, redirect line
• End-to-end: built and ran with host: 0.0.0.0 → banner lists Network URLs, lsof confirms *:port; host: 127.0.0.1 → banner shows loopback only
• go vet clean; internal/termout, internal/config, internal/app tests pass

Note for the reporter of #301: if LAN access still fails after this fix, the likely causes are firewall rules or the self-signed certificate warning (the in-memory cert SAN only covers localhost/127.0.0.1, which is documented behavior).