M4: split web UI assets into app.css and app.js

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/web/web_test.go

@@ -203,6 +203,33 @@ func TestActiveStatePayloadCarriesNudge(t *testing.T) {
 	}
 }
 
+func TestServesStaticAssets(t *testing.T) {
+	s := newTestServer(t)
+	r := s.Router()
+
+	cases := []struct {
+		path     string
+		ctSubstr string
+	}{
+		{"/app.css", "css"},
+		{"/app.js", "javascript"},
+	}
+	for _, tc := range cases {
+		req := httptest.NewRequest(http.MethodGet, tc.path, nil)
+		w := httptest.NewRecorder()
+		r.ServeHTTP(w, req)
+		if w.Code != http.StatusOK {
+			t.Errorf("GET %s code = %d, want 200", tc.path, w.Code)
+		}
+		if ct := w.Header().Get("Content-Type"); !strings.Contains(ct, tc.ctSubstr) {
+			t.Errorf("GET %s Content-Type = %q, want substring %q", tc.path, ct, tc.ctSubstr)
+		}
+		if w.Body.Len() == 0 {
+			t.Errorf("GET %s body is empty", tc.path)
+		}
+	}
+}
+
 func TestCommitmentCarriesAllowedClassesAndRoutesWork(t *testing.T) {
 	s := newTestServer(t)
 	r := s.Router()