fix: refine download cancellation logic to prevent accidental file deletion

- Update `AndroidDownloader` and `DesktopDownloader` to only delete local files if an active download was successfully cancelled.
- Move file deletion logic inside the active download check to ensure only incomplete files associated with a current session are removed.
- Simplify the `cancelDownload` return value to strictly reflect the cancellation status.

Author: rainxchzed

core/data/src/androidMain/kotlin/zed/rainxch/core/data/services/AndroidDownloader.kt

@@ -210,7 +210,6 @@ class AndroidDownloader(
     override suspend fun cancelDownload(fileName: String): Boolean =
         withContext(Dispatchers.IO) {
             var cancelled = false
-            var deleted = false
 
             val downloadId = activeFileNames[fileName]
             if (downloadId != null) {
@@ -222,13 +221,16 @@ class AndroidDownloader(
                     activeDownloads.remove(downloadId)
                 }
                 activeFileNames.remove(fileName)
-            }
 
-            val file = File(files.appDownloadsDir(), fileName)
-            if (file.exists()) {
-                deleted = file.delete()
+                // Only delete the file if we cancelled an active download (incomplete file)
+                if (cancelled) {
+                    val file = File(files.appDownloadsDir(), fileName)
+                    if (file.exists()) {
+                        file.delete()
+                    }
+                }
             }
 
-            cancelled || deleted
+            cancelled
         }
 }

core/data/src/jvmMain/kotlin/zed/rainxch/core/data/services/DesktopDownloader.kt

@@ -197,8 +197,6 @@ class DesktopDownloader(
     override suspend fun cancelDownload(fileName: String): Boolean =
         withContext(Dispatchers.IO) {
             var cancelled = false
-            var deleted = false
-
             val downloadId = nameToId[fileName]
             if (downloadId != null) {
                 activeDownloads[downloadId]?.let { call ->
@@ -209,14 +207,17 @@ class DesktopDownloader(
                 }
                 activeDownloads.remove(downloadId)
                 nameToId.remove(fileName)
-            }
 
-            val file = File(files.userDownloadsDir(), fileName)
-            if (file.exists()) {
-                deleted = file.delete()
+                // Only delete the file if we cancelled an active download (incomplete file)
+                if (cancelled) {
+                    val file = File(files.userDownloadsDir(), fileName)
+                    if (file.exists()) {
+                        file.delete()
+                    }
+                }
             }
 
-            cancelled || deleted
+            cancelled
         }
 
     companion object {