chore: add debug info when mutual pass search finds nothing

Shows pass count and satellite count in the error message to help
diagnose why the main pass list yields no results.

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualViewModel.kt

@@ -110,11 +110,23 @@ class MutualViewModel(
             val results = withContext(Dispatchers.Default) {
                 findMutualPasses(satellites, posA, posB, minElevA, minElevB, time, hours)
             }
+
+            val errorMsg = if (results.isEmpty()) {
+                // Debug: check if the main pass list is the culprit
+                val passCount = satelliteRepo.passes.value.size
+                val satCount = satellites.size
+                when {
+                    passCount == 0 -> "过境列表为空，请先在卫星列表中选择卫星"
+                    satCount == 0 -> "没有已选中的卫星"
+                    else -> "未找到共同过境（${passCount}个过境，${satCount}颗卫星）"
+                }
+            } else null
+
             _uiState.update {
                 it.copy(
                     mutualPasses = results.sortedBy { mp -> mp.startTime },
                     isCalculating = false,
-                    errorMessage = if (results.isEmpty()) "未找到共同过境" else null
+                    errorMessage = errorMsg
                 )
             }
         }