Security improvements, role in user creation, todo filters fix

- Remove better-auth dependency (unused)
- Update JWT secrets to stronger values
- Add ENCRYPTION_SALT env variable for password encryption
- Add role field to createUserSchema validator
- Accept role from body in admin.controller createUser
- Fix todo filters: add priority filter, handle completed param
- Remove .env.example (merged into .env)

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

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

src/routes/timesheet.routes.js

@@ -22,7 +22,7 @@ await fs.mkdir(uploadsDir, { recursive: true });
 const upload = multer({
   storage: multer.memoryStorage(),
   limits: {
-    fileSize: 10 * 1024 * 1024, // 10MB limit
+    fileSize: 5 * 1024 * 1024, // 5MB limit
   },
   fileFilter: (req, file, cb) => {
     const allowedTypes = ['application/pdf', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', 'application/vnd.ms-excel'];