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_static.wren

@@ -0,0 +1,33 @@
+// retoor <retoor@molodetz.nl>
+
+import "scheduler" for Scheduler, Future
+
+class Calculator {
+    static add { async { |a, b| a + b } }
+    static multiply { async { |a, b| a * b } }
+    static square { async { |x| x * x } }
+    static constant { async { 42 } }
+
+    static compute(a, b) {
+        var addFn = Calculator.add
+        var multiplyFn = Calculator.multiply
+        var sum = await addFn(a, b)
+        var product = await multiplyFn(a, b)
+        return [sum, product]
+    }
+}
+
+var add = Calculator.add
+System.print(await add(3, 4)) // expect: 7
+
+var multiply = Calculator.multiply
+System.print(await multiply(5, 6)) // expect: 30
+
+var square = Calculator.square
+System.print(await square(8)) // expect: 64
+
+var constant = Calculator.constant
+System.print(await constant()) // expect: 42
+
+var results = Calculator.compute(2, 3)
+System.print(results) // expect: [5, 6]