Docker improvements and decode loading state

- Fix .dockerignore to exclude *.img.xz files (was 2.3GB context)
- Remove deprecated 'version' attribute from docker-compose.yml
- Increase container memory limits to 2GB/1GB (prevent OOM on DCT)
- Add loading spinner to decode button during form submission

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.dockerignore

@@ -22,8 +22,10 @@ tests/
 # Pi-specific
 rpi/
 *.img
+*.img.xz
 *.img.zst
 *.img.zst.zip
+pishrink.sh
 
 # Docs
 *.md
@@ -37,3 +39,15 @@ docs/
 *.log
 *.tmp
 .DS_Store
+
+# Dev scripts and old files
+scripts/
+old_files/
+*_old
+*_old.*
+*.bak
+*.orig
+
+# Temp files
+frontends/web/temp_files/
+*.db