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_chain.wren

@@ -0,0 +1,54 @@
+// retoor <retoor@molodetz.nl>
+
+import "scheduler" for Scheduler, Future
+
+class DataProcessor {
+    static parse { async { |text| text.split(",") } }
+    static filter { async { |list, fn|
+        var result = []
+        for (item in list) {
+            if (fn.call(item)) result.add(item)
+        }
+        return result
+    }}
+    static transform { async { |list, fn|
+        var result = []
+        for (item in list) {
+            result.add(fn.call(item))
+        }
+        return result
+    }}
+    static join { async { |list, sep| list.join(sep) } }
+
+    static pipeline(data) {
+        var parse = DataProcessor.parse
+        var filter = DataProcessor.filter
+        var transform = DataProcessor.transform
+        var join = DataProcessor.join
+        var parsed = await parse(data)
+        var filtered = await filter(parsed) { |s| s.count > 4 }
+        var transformed = await transform(filtered) { |s| s.toList[0] }
+        return await join(transformed, "-")
+    }
+}
+
+var data = "apple,banana,cherry,date"
+
+var parse = DataProcessor.parse
+var parsed = await parse(data)
+System.print(parsed) // expect: [apple, banana, cherry, date]
+
+var filter = DataProcessor.filter
+var filtered = await filter(parsed) { |s| s.count > 5 }
+System.print(filtered) // expect: [banana, cherry]
+
+var transform = DataProcessor.transform
+var transformed = await transform(filtered) { |s| s.toList[0] }
+System.print(transformed) // expect: [b, c]
+
+var join = DataProcessor.join
+var joined = await join(transformed, "-")
+System.print(joined) // expect: b-c
+
+var result = DataProcessor.pipeline("one,two,three,four,five")
+System.print(result) // expect: t