test: Phase 113 if-only partial assign fixture + smokes (VM + LLVM)

- Add apps/tests/phase113_if_only_partial_assign_min.hako
  * Pattern: x=1; if flag==1 { x=2 } print(x)
  * Tests "preserve merge" on else side
- Add VM smoke: phase113_if_only_partial_assign_vm.sh
- Add LLVM EXE smoke: phase113_if_only_partial_assign_llvm_exe.sh
- Expected output: 1\n2 (flag=0 preserves, flag=1 updates)

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

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

apps/tests/phase113_if_only_partial_assign_min.hako

@@ -0,0 +1,27 @@
+// Phase 113: if-only partial assign (preserve merge on else side)
+
+static box Main {
+  main() {
+    local x
+    local flag
+
+    // First call: flag=0 → x stays 1 → print 1
+    flag = 0
+    x = 1
+    if flag == 1 {
+      x = 2
+    }
+    // else側は暗黙の "保持" (x keeps original value)
+    print(x)
+
+    // Second call: flag=1 → x becomes 2 → print 2
+    flag = 1
+    x = 1
+    if flag == 1 {
+      x = 2
+    }
+    print(x)
+
+    return "OK"
+  }
+}