fix(0117): pointer-to-array indexing auto-derefs

A '*[N]T' receiver in an index expression reached LLVM emission with an
unresolved element type and tripped the panic sentinel — no read or
write spelling worked. ptrToArrayElem on Lowering recognises the shape;
the index READ path GEPs the pointee array through the pointer value
and loads the element; the write / compound-assign / lvalue /
addr-of-element paths and the expression typer resolve the element type
through the same helper (their GEP machinery already handled a pointer
base). Kept out of getElementType so slice paths don't half-accept a
raw pointer base.

Regression: examples/0176 (read, write, compound, element ptr + deref).

src/ir/lower/expr.zig

@@ -1263,6 +1263,12 @@ pub fn lowerIndexExpr(self: *Lowering, ie: *const ast.IndexExpr) Ref {
     const idx = self.lowerExpr(ie.index);
     // Infer element type from the object's slice/array type
     const obj_ty = self.inferExprType(ie.object);
+    // `*[N]T` receiver auto-derefs (issue 0117): `obj` IS the pointer
+    // value — GEP the pointee array and load the element.
+    if (self.ptrToArrayElem(obj_ty)) |elem| {
+        const gep = self.builder.emit(.{ .index_gep = .{ .lhs = obj, .rhs = idx } }, self.module.types.ptrTo(elem));
+        return self.builder.load(gep, elem);
+    }
     const elem_ty = self.getElementType(obj_ty);
     return self.builder.emit(.{ .index_get = .{ .lhs = obj, .rhs = idx } }, elem_ty);
 }
@@ -1843,7 +1849,7 @@ pub fn lowerExpr(self: *Lowering, node: *const Node) Ref {
                 const ie = &uop.operand.data.index_expr;
                 const idx = self.lowerExpr(ie.index);
                 const obj_ty = self.inferExprType(ie.object);
-                const elem_ty = self.getElementType(obj_ty);
+                const elem_ty = self.ptrToArrayElem(obj_ty) orelse self.getElementType(obj_ty);
                 const ptr_ty = self.module.types.ptrTo(elem_ty);
                 // For array targets, use the storage pointer (alloca for a
                 // local, global_addr for a module global) so the resulting