selfhost: for x in collection works with non-identifier expressions + buxc2 build merges stdlib

- cli: buxc2 build now delegates to Cli_BuildProject for src/Main.bux,
  enabling stdlib merging (Array_Iter, Iter_HasNext, etc. available)
- sema: set expr.refType on ekCall from function return type
  (needed for for-loop type extraction from MakeArr()-style expressions)
- hir_lower: remove ekIdent restriction on collection-based for loops
  - supports arbitrary expressions: for x in MakeArr() { ... }
  - creates temp variable __tmp_coll_N for non-identifier iterators
  - generates proper Array_T struct instances for temp variables
- Test: for x in MakeArr() sums [10,20,30] → 60
- Selfhost loop: C output IDENTICAL

src/sema.bux

@@ -579,6 +579,7 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
         if calleeType == tyFunc {
             if expr.child1.refType != null as *TypeExpr && expr.child1.refType.kind == tekFunc {
                 if expr.child1.refType.funcRet != null as *TypeExpr {
+                    expr.refType = expr.child1.refType.funcRet;
                     return Sema_ResolveType(sema, expr.child1.refType.funcRet);
                 }
                 return tyVoid;
@@ -589,6 +590,7 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
             let sym: Symbol = Scope_Lookup(sema.scope, expr.child1.strValue);
             if sym.kind == skFunc && sym.decl != null as *Decl {
                 if sym.decl.retType != null as *TypeExpr {
+                    expr.refType = sym.decl.retType;
                     return Sema_ResolveType(sema, sym.decl.retType);
                 }
             }