fix(bootstrap): resolve lir lower crashes and struct-copy bugs

- Fix lirValToC crash on lvkInt in hStore raw C emission
- Add hAlloca handling to lowerExpr (returns &name, avoids unhandled fallback)
- Fix nested comment syntax in unhandled expr fallback
- Rewrite buildLval to handle hIndexPtr and nested hFieldPtr/hArrowField
  so assignments like arr[i].field = val emit direct C lvalues
- Make &&/|| temporaries unique (__and_tmp_N/__or_tmp_N) to avoid
  duplicate declarations in the same function
- Selfhost null-deref fix in sema.bux (unchained nested conditions)

src/sema.bux

@@ -239,9 +239,13 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
         // Try to resolve return type from function declaration
         if expr.child1.kind == ekIdent {
             let sym: Symbol = Scope_Lookup(sema.scope, expr.child1.strValue);
-            if sym.kind == skFunc && sym.decl != null as *Decl && sym.decl.retType != null as *TypeExpr {
+            if sym.kind == skFunc {
+            if sym.decl != null as *Decl {
+            if sym.decl.retType != null as *TypeExpr {
                 return Sema_ResolveType(sema, sym.decl.retType);
             }
+            }
+            }
         }
         return tyUnknown;
     }