fix: Base the disk space check on remaining bytes when resuming

The check ran before resume state was read and always demanded 1.5x the
full APK size. Bytes already sitting in download_temp.apk have already
consumed storage, so on a low-storage device an interrupted download
could fail every resume with "Insufficient storage" even when only a
small tail was left to fetch.

Read the resume state first and check space for the remaining bytes
only. A fresh download still checks the full size, and a complete temp
file needs no extra space since promotion is a rename.

Addresses the Codex review finding on UniversalApkManager.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/com/bitchat/android/util/UniversalApkManager.kt

@@ -219,9 +219,6 @@ class UniversalApkManager(private val context: Context) {
             Log.d(TAG, "Downloading from: $url")
             Log.d(TAG, "Expected size: ${expectedSize / 1024 / 1024}MB")
 
-            // Check available disk space before downloading
-            checkDiskSpace(expectedSize)
-
             val tempFile = File(cacheDir, "download_temp.apk")
 
             // Check for resumable download
@@ -241,6 +238,11 @@ class UniversalApkManager(private val context: Context) {
                 }
             }
 
+            // Bytes already in the temp file have already consumed storage, so
+            // a resume only needs room for the remaining tail. Promotion is a
+            // rename and needs no extra space.
+            checkDiskSpace((expectedSize - existingBytes).coerceAtLeast(0))
+
             // A temp file that already holds the full asset means the process
             // died between download and verification. Requesting
             // "Range: bytes=<size>-" for it would get HTTP 416 forever, so skip