Embed web assets into the Go binary

Serve /static from embedded assets when no static path override is configured, add static route coverage, and update Docker/docs to reflect embedded-by-default behavior.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

go/webterm/assets_embed.go

@@ -0,0 +1,18 @@
+package webterm
+
+import (
+	"embed"
+	"io/fs"
+	"net/http"
+)
+
+//go:embed static static/* static/js/* static/icons/*
+var embeddedStaticAssets embed.FS
+
+func embeddedStaticFS() (http.FileSystem, bool) {
+	sub, err := fs.Sub(embeddedStaticAssets, "static")
+	if err != nil {
+		return nil, false
+	}
+	return http.FS(sub), true
+}