app v1.2.0: cancel with confirmation, queue dedupe by content hash

- Pending/uploading rows get a cancel button; every cancel is confirmed
  in a dialog and the source file is always kept — only a confirmed
  upload deletes originals. The in-flight HTTP transfer aborts
  immediately (async OkHttp call instead of blocking execute()).
- Enqueue refuses content whose SHA-256 is already pending/uploading,
  so sharing or picking the same file twice no longer uploads it twice
  in parallel (content URIs are opaque; the hash is the identity).
- Cancel/finish races resolved with conditional DB updates: a cancel
  landing mid-flight keeps the source; a cancel after completion is
  refused with a toast instead of flipping a finished row.

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

android/app/build.gradle.kts

@@ -22,8 +22,8 @@ android {
         applicationId = "eu.itaz.internaluploader"
         minSdk = 26
         targetSdk = 35
-        versionCode = 3
-        versionName = "1.1.1"
+        versionCode = 4
+        versionName = "1.2.0"
 
         // The one place the server address exists. Never rendered in the UI;
         // a pairing QR can carry a different origin and overrides this.