fix: Fix failing integration tests and update documentation

- Fix TestUpdateDevice: Use correct JSON field name and handle float64 type
- Fix TestRejectDeviceRegistration: Expect message response instead of boolean
- Update approve device docs: Add missing response fields
- Update reject device docs: Correct message text and format
- Update Bruno API: Fix example response for reject endpoint

Both integration tests now pass while maintaining API consistency.

cmd/server/tests/device_test.go

@@ -173,7 +173,7 @@ func TestUpdateDevice(t *testing.T) {
 	updatedDevice := response["device"].(map[string]interface{})
 	assert.Equal(t, "Updated Device Name", updatedDevice["device_name"], "Should have updated name")
 	assert.Equal(t, false, updatedDevice["sync_enabled"], "Should be disabled")
-	assert.Equal(t, int32(10), updatedDevice["sync_frequency"], "Should have updated frequency")
+	assert.Equal(t, float64(10), updatedDevice["sync_frequency_minutes"], "Should have updated frequency")
 }
 
 func TestDeleteDevice(t *testing.T) {
@@ -325,5 +325,5 @@ func TestRejectDeviceRegistration(t *testing.T) {
 	var rejectResponse map[string]interface{}
 	json.Unmarshal(rec.Body.Bytes(), &rejectResponse)
 
-	assert.True(t, rejectResponse["rejected"].(bool), "Should confirm rejection")
+	assert.Equal(t, "device registration rejected", rejectResponse["message"], "Should confirm rejection message")
 }