Android: track download state to avoid duplicate update prompts

[fiddur]

Summary

• Persist download ID and version to SharedPreferences so the app can check download status across restarts
• On app open, query DownloadManager for existing downloads before showing the update dialog:
  • Completed download → show "Update Ready" dialog with Install button
  • In-progress download → show "Downloading" dialog instead of prompting again
  • No download → show normal "Update Available" dialog
• After a fresh download completes, show the "Update Ready" install dialog instead of auto-launching the installer

Test plan

• Install an older version, open the app, verify update dialog appears
• Click "Update", verify download starts and downloading dialog shows
• Dismiss downloading dialog, reopen app → should show downloading dialog (not update available)
• After download completes, reopen app → should show "Update Ready" install dialog
• Click "Install" → system installer launches
• Dismiss install dialog, reopen app → should show install dialog again (APK still present)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 0% with 80 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.26%. Comparing base (77dcc22) to head (344d1b8).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...c/main/java/net/aurboda/update/UpdateDownloader.kt	0.00%	42 Missing ⚠️
...roid/app/src/main/java/net/aurboda/MainActivity.kt	0.00%	22 Missing ⚠️
...p/src/main/java/net/aurboda/update/UpdateDialog.kt	0.00%	16 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #245      +/-   ##
===========================================
- Coverage    27.35%   27.26%   -0.09%     
===========================================
  Files          176      176              
  Lines        23674    23752      +78     
  Branches      2104     2122      +18     
===========================================
  Hits          6476     6476              
- Misses       17159    17237      +78     
  Partials        39       39              

Flag	Coverage Δ
android	8.57% <0.00%> (-0.18%)	⬇️
backend	57.58% <ø> (ø)
web	3.02% <ø> (ø)

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