start kotlin/jetpack compose rewrite

replace the flutter project with a gradle/compose android app:
- nix flake dev shell (jdk21, android sdk 35, build-tools 37, gradle)
- material3 app with a placeholder screen
- roborazzi/robolectric screenshot tests with one golden
- carry over the existing launcher/notification assets

tools/preview_server.py

@@ -0,0 +1,66 @@
+"""Serve the Roborazzi report for local review: thumbnails scaled by CSS and
+full images opened in a new tab. Expects a .preview/ directory mirroring the
+app module layout (build/reports/roborazzi and src/test/screenshots)."""
+
+import http.server
+import os
+import sys
+
+ROOT = os.path.normpath(
+    os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", ".preview")
+)
+
+INJECT = """
+<style>
+  img.thumb {
+    max-height: 220px;
+    width: auto;
+    height: auto !important;
+    object-fit: contain !important;
+    cursor: zoom-in;
+  }
+</style>
+<script>
+  document.querySelectorAll('img.modal-trigger').forEach(function (img) {
+    var src = img.getAttribute('src');
+    var clean = img.cloneNode(false);
+    clean.className = 'thumb';
+    clean.setAttribute('src', src);
+    clean.removeAttribute('data-alt');
+    var a = document.createElement('a');
+    a.href = src;
+    a.target = '_blank';
+    a.rel = 'noopener';
+    a.appendChild(clean);
+    img.parentNode.replaceChild(a, img);
+  });
+</script>
+"""
+
+
+class Handler(http.server.SimpleHTTPRequestHandler):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, directory=ROOT, **kwargs)
+
+    def do_GET(self):
+        path = self.translate_path(self.path)
+        if os.path.isdir(path):
+            path = os.path.join(path, "index.html")
+        if os.path.isfile(path) and path.endswith(".html"):
+            with open(path, "r", encoding="utf-8") as f:
+                html = f.read()
+            html = html.replace("</body>", INJECT + "</body>")
+            body = html.encode("utf-8")
+            self.send_response(200)
+            self.send_header("Content-Type", "text/html; charset=utf-8")
+            self.send_header("Content-Length", str(len(body)))
+            self.end_headers()
+            self.wfile.write(body)
+            return
+        super().do_GET()
+
+
+if __name__ == "__main__":
+    port = int(sys.argv[1]) if len(sys.argv) > 1 else 8099
+    server = http.server.ThreadingHTTPServer(("127.0.0.1", port), Handler)
+    server.serve_forever()