ffi 2.2 green: parser collects #jni_class instance method body items

New `JniMethodDecl` AST struct (name, params, param_names,
return_type — no body, foreign declaration). `JniClassDecl.body`
becomes `methods: []const JniMethodDecl`. parseJniClassDecl loops
over body items, parsing each `name :: (self: *Self, args...) -> Ret;`
similarly to parseProtocolDecl but requiring `;` (no body brace).

`static`, fields, `#extends`, `#implements`, and the other six
directive forms land in 2.3–2.7. Sema/lower still treat the decl
as an opaque type alias — descriptor derivation arrives in 2.8+.

121/121 examples green.

src/ast.zig

@@ -533,10 +533,17 @@ pub const ProtocolDecl = struct {
     type_params: []const StructTypeParam = &.{}, // for `protocol(Target: Type) { ... }`
 };
 
+pub const JniMethodDecl = struct {
+    name: []const u8,
+    params: []const *Node, // type_expr nodes — first is `*Self` for instance methods
+    param_names: []const []const u8,
+    return_type: ?*Node, // null = void
+};
+
 pub const JniClassDecl = struct {
     name: []const u8, // sx-side alias (left of `::`)
     java_path: []const u8, // directive arg, e.g. "java/path/Foo"
-    body: []const *Node = &.{}, // body items (methods, fields, #extends, ...) — empty in 2.1
+    methods: []const JniMethodDecl = &.{}, // instance methods (static/fields/extends land in later steps)
 };
 
 pub const ImplBlock = struct {