Auto-increment folder name if staging folder already exists

StagingPath.uniqueFolderName() checks whether the base folder name is
already taken and appends _2, _3, etc. until a free name is found.
AppState.prepareImport() now uses this so the ImportScreen always
pre-fills a unique folder name.

src/main/kotlin/com/bolenpad/photophetch/ui/AppState.kt

@@ -220,10 +220,19 @@ class AppState(
 
     fun prepareImport() {
         val device = _selectedDevice.value ?: return
+        val cfg = _config.value
         val today = LocalDate.now()
-        val folderName = _config.value.folderNameTemplate
+        val baseName = cfg.folderNameTemplate
             .replace("{date}", today.toString())
             .replace("{device}", StagingPath.deviceLabel(device))
+
+        // Auto-increment if the folder already exists: 2026-07-28_iPhone15Pro_2, _3, …
+        val folderName = if (cfg.stagingRoot.isNotBlank()) {
+            StagingPath.uniqueFolderName(Paths.get(cfg.stagingRoot), baseName)
+        } else {
+            baseName
+        }
+
         _importConfig.update { it.copy(folderName = folderName) }
         navigateTo(Screen.IMPORT_CONFIG)
     }

src/main/kotlin/com/bolenpad/photophetch/util/StagingPath.kt

@@ -49,6 +49,26 @@ object StagingPath {
         return stagingRoot.resolve(folderName)
     }
 
+    /**
+     * Returns a folder name that doesn't already exist under [stagingRoot].
+     * If the base name is free, returns it as-is.
+     * If it already exists, appends _2, _3, … until a free name is found.
+     *
+     * Examples:
+     *   "2026-07-28_iPhone15Pro"       → free → returns as-is
+     *   "2026-07-28_iPhone15Pro" taken → returns "2026-07-28_iPhone15Pro_2"
+     *   "2026-07-28_iPhone15Pro_2" taken → returns "2026-07-28_iPhone15Pro_3"
+     */
+    fun uniqueFolderName(stagingRoot: Path, baseName: String): String {
+        if (!stagingRoot.resolve(baseName).exists()) return baseName
+        var counter = 2
+        while (true) {
+            val candidate = "${baseName}_$counter"
+            if (!stagingRoot.resolve(candidate).exists()) return candidate
+            counter++
+        }
+    }
+
     /**
      * Create the staging directory if it doesn't already exist.
      * @throws IllegalStateException if the parent is not writable