Fix test infrastructure and device UUID handling

- Remove manual device ID generation, use database-generated IDs
- Add comprehensive test helpers (setupTestServer, loginTestUser, getTestUserID)
- Add cleanup step for existing test users in integration tests
- Fix UUID parsing from database responses

cmd/server/tests/phase1_integration_test.go

@@ -20,6 +20,79 @@ func TestPhase1Integration(t *testing.T) {
 		t.Skip("Skipping integration test in short mode")
 	}
 
+	// Cleanup: Try to delete test user if it exists from previous test runs
+	t.Run("Cleanup_ExistingTestUser", func(t *testing.T) {
+		// Try to login as the test user first
+		loginReq := map[string]interface{}{
+			"login":    "admin@bookmann.test",
+			"password": "SecurePass123!",
+		}
+
+		body, _ := json.Marshal(loginReq)
+		resp, err := http.Post(baseTestURL+"/auth/login", "application/json", bytes.NewBuffer(body))
+		if err != nil {
+			t.Logf("Cleanup: No existing test user to delete (server not available)")
+			return
+		}
+		defer resp.Body.Close()
+
+		// If login succeeds, try to delete the user
+		if resp.StatusCode == http.StatusOK {
+			var result map[string]interface{}
+			json.NewDecoder(resp.Body).Decode(&result)
+
+			if token, ok := result["access_token"].(string); ok {
+				// Delete the user using the token
+				req, _ := http.NewRequest("DELETE", baseTestURL+"/auth/account", bytes.NewBuffer([]byte{}))
+				req.Header.Set("Authorization", "Bearer "+token)
+				req.Header.Set("Content-Type", "application/json")
+
+				client := &http.Client{}
+				delResp, err := client.Do(req)
+				if err == nil {
+					defer delResp.Body.Close()
+					if delResp.StatusCode == http.StatusNoContent {
+						t.Logf("Cleanup: Deleted existing test user")
+					} else {
+						t.Logf("Cleanup: Could not delete existing test user (HTTP %d)", delResp.StatusCode)
+					}
+				}
+
+				// Also try to delete any libraries created by this user
+				req, _ = http.NewRequest("GET", baseTestURL+"/libraries", bytes.NewBuffer([]byte{}))
+				req.Header.Set("Authorization", "Bearer "+token)
+
+				listResp, err := client.Do(req)
+				if err == nil {
+					defer listResp.Body.Close()
+					if listResp.StatusCode == http.StatusOK {
+						var libsResult map[string]interface{}
+						json.NewDecoder(listResp.Body).Decode(&libsResult)
+
+						if data, ok := libsResult["data"].([]interface{}); ok {
+							for _, lib := range data {
+								if libMap, ok := lib.(map[string]interface{}); ok {
+									if libID, ok := libMap["id"].(string); ok {
+										// Delete the library
+										req, _ = http.NewRequest("DELETE", baseTestURL+"/libraries/"+libID, bytes.NewBuffer([]byte{}))
+										req.Header.Set("Authorization", "Bearer "+token)
+										delLibResp, _ := client.Do(req)
+										if delLibResp != nil {
+											delLibResp.Body.Close()
+										}
+									}
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+
+		// Wait a bit for cleanup to complete
+		time.Sleep(500 * time.Millisecond)
+	})
+
 	// Step 1: Create first user (should be admin)
 	t.Run("Step1_CreateFirstUser", func(t *testing.T) {
 		userReq := map[string]interface{}{