Simplify code based on final review feedback

- Use direct character assignment for constant strings
- Remove unnecessary tracking array and cleanup code
- Simplify string concatenation logic
- Fix length calculation to match actual strncat behavior
- Code is cleaner and more maintainable

Co-authored-by: squassina <8495707+squassina@users.noreply.github.com>

src/fetch/common.h

@@ -77,9 +77,9 @@ void get_layout_abbr(char *abbr, const char *full_name) {
 		abbr[2] = '\0';
 	} else {
 		// 5. 最终回退：返回 "xx"
-		// Explicit null termination for consistency
-		strncpy(abbr, "xx", LAYOUT_ABBR_SIZE - 1);
-		abbr[LAYOUT_ABBR_SIZE - 1] = '\0';
+		abbr[0] = 'x';
+		abbr[1] = 'x';
+		abbr[2] = '\0';
 	}
 }