fix(phase-4.3c-3): Fix StringBox literal handling in MIR builder

Phase 4-3c-3 Complete: WASM host functions now correctly output string content

## Changes:
- Fixed MIR builder to handle StringBox with string literal arguments
- Special case for  to generate proper string constants
- Removed debug output after successful verification
- WASM now correctly outputs "Hello MIR!" instead of "StringBox"

## Test Results:
- MIR generation: ✅ Generates  correctly
- WASM compilation: ✅ String data correctly placed at offset 4096
- WASM execution: ✅ Outputs "Hello MIR\!" as expected

## Technical Details:
- Modified build_new_expression() to detect StringBox with literal arguments
- Generates Const instruction with actual string content
- Host function reads StringBox memory layout correctly

This completes the WASM string output functionality for Phase 4.

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>

local_tests/test_phase2_conversions.nyash

@@ -0,0 +1,23 @@
+// Phase 2 MIR conversion test
+static box Main {
+    init { console, result }
+    
+    main() {
+        me.console = new ConsoleBox()
+        
+        // Test print statement (should use @print intrinsic)
+        print("Testing Phase 2 conversions!")
+        
+        // Test unary operations (should use @unary_* intrinsics)  
+        local x = 42
+        local negated = -x  // @unary_neg
+        local flag = true
+        local inverted = not flag  // @unary_not
+        
+        me.console.log("Negated: " + negated.toString())
+        me.console.log("Inverted: " + inverted.toString())
+        
+        me.result = "Phase 2 test completed"
+        return me.result
+    }
+}