feat: add await syntax for direct async function calls and new generator/phonebook apps

Add compiler support for calling async functions directly with `await fn(args)` syntax, automatically translating to `await fn.call(args)`. Introduce `create_merge` Makefile target for merging Wren source files. Include new `apps/generator.wren` source code generator using OpenRouter API, `apps/phonebook.wren` CLI phonebook with SQLite backend, and `apps/minitut.md` Wren tutorial reference. Update `example/await_demo.wren` with parameterized async functions, nested awaits, and expression usage. Fix JSON parsing in `example/openrouter_demo.wren` to strip markdown code fences. Document new await syntax in `manual/api/scheduler.html`.

test/await/await_fn_class_api.wren

@@ -0,0 +1,50 @@
+// retoor <retoor@molodetz.nl>
+
+import "scheduler" for Scheduler, Future
+import "timer" for Timer
+
+class MockApi {
+    static fetchUser { async { |id|
+        Timer.sleep(1)
+        return {"id": id, "name": "User%(id)", "active": true}
+    }}
+
+    static fetchPosts { async { |userId|
+        Timer.sleep(1)
+        return [
+            {"id": 1, "userId": userId, "title": "Post 1"},
+            {"id": 2, "userId": userId, "title": "Post 2"}
+        ]
+    }}
+
+    static createPost { async { |userId, title|
+        Timer.sleep(1)
+        return {"id": 3, "userId": userId, "title": title, "created": true}
+    }}
+
+    static getUserWithPosts(userId) {
+        var fetchUser = MockApi.fetchUser
+        var fetchPosts = MockApi.fetchPosts
+        var user = await fetchUser(userId)
+        var posts = await fetchPosts(userId)
+
+        user["posts"] = posts
+        return user
+    }
+}
+
+var fetchUser = MockApi.fetchUser
+var user = await fetchUser(42)
+System.print(user["name"]) // expect: User42
+
+var fetchPosts = MockApi.fetchPosts
+var posts = await fetchPosts(42)
+System.print(posts.count) // expect: 2
+
+var createPost = MockApi.createPost
+var newPost = await createPost(42, "New Post")
+System.print(newPost["created"]) // expect: true
+
+var fullUser = MockApi.getUserWithPosts(99)
+System.print(fullUser["name"]) // expect: User99
+System.print(fullUser["posts"].count) // expect: 2