Add app source and tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

bricks/mvvc_template/brick.yaml

@@ -0,0 +1,21 @@
+name: mvvc_template
+description: Generates a Peach screen as the mandatory four files — the
+  StatefulWidget shell, its State (UI + Connect implementation), the ViewModel
+  (logic, talks to the DataManager) and the Connect interface between them.
+
+version: 0.1.0+1
+
+environment:
+  mason: ^0.1.1
+
+vars:
+  project:
+    type: string
+    description: The top-level folder under lib/ (also the package name)
+    default: Peach
+    prompt: What is your project name?
+  screen:
+    type: string
+    description: The screen name in PascalCase, e.g. ServerDetail
+    default: NewScreen
+    prompt: What is your screen name?