refactor: rename inspect to replay across the codebase

Renames inspect-ui/ to replay-ui/, internal/inspect/ to internal/replay/,
the CLI subcommand from `sanderling inspect` to `sanderling replay`, and
updates all references in docs, Makefile, README, and Go comments.

internal/replay/dev.go

@@ -0,0 +1,20 @@
+package replay
+
+import (
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+)
+
+// DevTarget is the hardcoded Vite dev server address. The --dev flag
+// enables a reverse proxy to this address for non-API requests.
+const DevTarget = "http://127.0.0.1:5173"
+
+func newDevProxy(target string) (http.Handler, error) {
+	parsed, err := url.Parse(target)
+	if err != nil {
+		return nil, err
+	}
+	proxy := httputil.NewSingleHostReverseProxy(parsed)
+	return proxy, nil
+}