Fix file upload limits and UI performance issues

- Remove artificial 18MB file size restrictions across all layers
- Increase limits to industry standard: 5GB for file operations, 1GB for JSON
- Eliminate duplicate resize handlers causing UI instability
- Fix Terminal connection blank screen by removing 300ms delay
- Optimize clipboard state flow for copy/paste functionality
- Complete i18n implementation removing hardcoded strings
- Apply Linus principle: eliminate complexity, fix data structure issues

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

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

src/backend/database/database.ts

@@ -46,7 +46,7 @@ const storage = multer.diskStorage({
 const upload = multer({
   storage: storage,
   limits: {
-    fileSize: 100 * 1024 * 1024, // 100MB limit
+    fileSize: 1024 * 1024 * 1024, // 1GB limit for database operations
   },
   fileFilter: (req, file, cb) => {
     // Allow SQLite files