ffi 2.5 green: name: Type; field body items in #jni_class

New `JniFieldDecl` AST struct (name + field_type); `JniClassMember`
gains a `field` variant. After consuming a member-name identifier
in the body loop, the parser branches on the next token: `:` →
field path (parse type expr + `;`), `::` → method path (existing).

`static` fields aren't part of the grammar yet and error explicitly
("static fields not yet supported"); only instance fields land here.
Lowering to JNI `Get<Type>Field` / `Set<Type>Field` arrives in 2.13.

124/124 examples green.

src/parser.zig

@@ -1071,13 +1071,28 @@ pub const Parser = struct {
                 self.advance(); // consume `static`
             }
 
+            // Field: name: Type;       (instance field — JNI Get/Set<Type>Field)
             // Method: name :: (args...) -> Ret;
-            // (Fields, #desc override land in later steps.)
             if (self.current.tag != .identifier) {
-                return self.fail("expected method name in '#jni_class' body");
+                return self.fail("expected member name in '#jni_class' body");
             }
-            const method_name = self.tokenSlice(self.current);
+            const member_name = self.tokenSlice(self.current);
             self.advance();
+
+            if (self.current.tag == .colon) {
+                if (is_static) {
+                    return self.fail("static fields not yet supported in '#jni_class' body");
+                }
+                self.advance(); // consume `:`
+                const field_type = try self.parseTypeExpr();
+                try self.expect(.semicolon);
+                try members.append(self.allocator, .{ .field = .{
+                    .name = member_name,
+                    .field_type = field_type,
+                } });
+                continue;
+            }
+
             try self.expect(.colon_colon);
             try self.expect(.l_paren);
 
@@ -1109,7 +1124,7 @@ pub const Parser = struct {
             try self.expect(.semicolon);
 
             try members.append(self.allocator, .{ .method = .{
-                .name = method_name,
+                .name = member_name,
                 .params = try param_types.toOwnedSlice(self.allocator),
                 .param_names = try param_names.toOwnedSlice(self.allocator),
                 .return_type = return_type,