revert: completely remove all Sora functionality

backend/internal/web/embed_on.go

@@ -256,7 +256,6 @@ func shouldBypassEmbeddedFrontend(path string) bool {
 	return strings.HasPrefix(trimmed, "/api/") ||
 		strings.HasPrefix(trimmed, "/v1/") ||
 		strings.HasPrefix(trimmed, "/v1beta/") ||
-		strings.HasPrefix(trimmed, "/sora/") ||
 		strings.HasPrefix(trimmed, "/antigravity/") ||
 		strings.HasPrefix(trimmed, "/setup/") ||
 		trimmed == "/health" ||

backend/internal/web/embed_test.go

@@ -434,7 +434,6 @@ func TestFrontendServer_Middleware(t *testing.T) {
 			"/api/v1/users",
 			"/v1/models",
 			"/v1beta/chat",
-			"/sora/v1/models",
 			"/antigravity/test",
 			"/setup/init",
 			"/health",
@@ -637,7 +636,6 @@ func TestServeEmbeddedFrontend(t *testing.T) {
 			"/api/users",
 			"/v1/models",
 			"/v1beta/chat",
-			"/sora/v1/models",
 			"/antigravity/test",
 			"/setup/init",
 			"/health",