chore(test): Improve phase246ex_atoi_mini test format

- Change from string return ("PASS"/"FAIL") to numeric RC (0=success, 1=fail)
- Add print("result = N") for stdout verification
- Update comments to reflect new test format

This makes test results verifiable via both stdout AND return code,
avoiding future confusion about RC interpretation.

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

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

apps/tests/phase246ex_atoi_mini.hako

@@ -1,5 +1,6 @@
 // Phase 246-EX: Minimal _atoi test
 // Tests NumberAccumulation pattern: result = result * 10 + digit_pos
+// Prints "result = N" to stdout, returns 0 on success (42), 1 on failure.
 
 static box Phase246ExAtoiMini {
     main() {
@@ -8,10 +9,11 @@ static box Phase246ExAtoiMini {
         local result = me.atoi(s, len)
 
         // Expected: 42
+        print("result = " + result)
         if result == 42 {
-            return "PASS"
+            return 0
         } else {
-            return "FAIL"
+            return 1
         }
     }