Add optional web UI mirroring --monitor (LISTEN_UI, off by default)

A single self-contained page polls /api/status once a second and renders
the same lines as the terminal monitor (downstreams with models/VRAM and
busy markers, lock, queue, GPU stats); the u/r buttons and keys trigger
update-now and reload-env through the same rate-limited command handler
the control pipe uses. Unauthenticated by design — the sample config
tells users to keep it on localhost.

internal/config/config.go

@@ -19,6 +19,7 @@ import (
 type Config struct {
 	ListenOllama   string        `env:"LISTEN_OLLAMA"`
 	ListenComfy    string        `env:"LISTEN_COMFY"`
+	ListenUI       string        `env:"LISTEN_UI"`
 	OllamaURL      string        `env:"OLLAMA_URL"`
 	ComfyURL       string        `env:"COMFY_URL"`
 	UnloadTimeout  time.Duration `env:"UNLOAD_TIMEOUT"`
@@ -196,6 +197,7 @@ func Load(getenv func(string) string) (Config, error) {
 	}{
 		{"LISTEN_OLLAMA", &cfg.ListenOllama},
 		{"LISTEN_COMFY", &cfg.ListenComfy},
+		{"LISTEN_UI", &cfg.ListenUI},
 		{"OLLAMA_URL", &cfg.OllamaURL},
 		{"COMFY_URL", &cfg.ComfyURL},
 		{"WARM_MODEL", &cfg.WarmModel},