ffi M2.1(a): class-level constants 'name :: Type = expr;'

Inside a '#objc_class { ... }' block, 'name :: Type = expr;' is
accepted alongside the existing method form. Parsed as sugar for
'name :: () -> Type => expr;' — a niladic class method with an
expression body. The synthesized class method flows through the
M2.1(b) class-method pipeline: a C-ABI IMP is emitted and
registered on the metaclass.

Apple's runtime sees zero distinction — '[Cls foo]' dispatches to
our IMP regardless of source spelling. The constant form is
purely syntactic sugar; it reads better for static metadata
returns:

  SxGLView :: #objc_class("SxGLView") {
      layerClass :: Class = CAEAGLLayer.class();
  }

vs. the equivalent method form:

  layerClass :: () -> Class => CAEAGLLayer.class();

Parser change: after 'name ::' if the next token isn't '(' we
take the constant branch — parse a type expr, expect '=', parse
the value expr, expect ';'. The result is a ForeignMethodDecl
with is_static=true, empty params, return_type=Type, body=block
wrapping the expr. Pure parser-level transformation; no new AST
nodes, no new lowering passes.

150-objc-class-level-constant.sx exercises both shapes on macOS:
a primitive (s32 answer) and a pointer ('*NSObject seedClass'
— the canonical '+layerClass'-style factory return).

180 example tests pass (+1). zig build test green.

M2.1 complete: both (a) the constant form and (b) the
expression-bodied class method shape land.

Next: M2.2 — 'field: T #property(modifiers...)' synthesizes
getter/setter pairs.

src/parser.zig

@@ -1183,6 +1183,36 @@ pub const Parser = struct {
             }
 
             try self.expect(.colon_colon);
+
+            // M2.1(a) — class-level constant `name :: Type = expr;` inside
+            // a `#objc_class` block. Reframed as a synthesized class method
+            // with an expression body (`name :: () -> Type => expr;`) so
+            // the rest of the M1.2 class-synthesis pipeline picks it up:
+            // a class-method IMP is emitted and registered on the metaclass.
+            // Apple's runtime calls the IMP from `[Cls foo]` — there's no
+            // runtime-level distinction between a class-level constant and
+            // a niladic class method, just a difference in source spelling.
+            if (self.current.tag != .l_paren) {
+                const ret_type = try self.parseTypeExpr();
+                try self.expect(.equal);
+                const expr_node = try self.parseExpr();
+                try self.expect(.semicolon);
+                const stmts = try self.allocator.alloc(*Node, 1);
+                stmts[0] = expr_node;
+                const block_node = try self.createNode(expr_node.span.start, .{ .block = .{ .stmts = stmts } });
+                try members.append(self.allocator, .{ .method = .{
+                    .name = member_name,
+                    .params = &.{},
+                    .param_names = &.{},
+                    .return_type = ret_type,
+                    .is_static = true,
+                    .jni_descriptor_override = null,
+                    .selector_override = null,
+                    .body = block_node,
+                } });
+                continue;
+            }
+
             try self.expect(.l_paren);
 
             var param_types = std.ArrayList(*Node).empty;