fix: allow HTTP to local instances in release build; fix activity 404 in dev

Android release builds block cleartext HTTP by default (debug builds override
this via the debug manifest overlay). Add usesCleartextTraffic=true to app.json
so expo prebuild includes it in the generated manifest — required to reach local
Bincio instances over HTTP.

In bincio dev (Astro dev server), /activity/<id>/ routes 404 because
getStaticPaths() returns [] and there is no nginx try_files fallback. Add a Vite
middleware plugin to astro.config.mjs that rewrites /activity/<id>/ to /activity/
in dev, matching what nginx does in production.

site/astro.config.mjs

@@ -9,6 +9,20 @@ const env = loadEnv(process.env.NODE_ENV ?? 'development', process.cwd(), '');
 const apiPort = process.env.VITE_API_PORT || '4041';
 const serveTarget = env.PUBLIC_EDIT_URL || `http://localhost:${apiPort}`;
 
+// In production, nginx serves activity/index.html for all /activity/<id>/ URLs
+// via try_files. In dev (Astro dev server), no nginx — this plugin replicates it.
+const activityFallbackPlugin = {
+  name: 'activity-shell-fallback',
+  configureServer(server) {
+    server.middlewares.use((req, _res, next) => {
+      if (req.url && /^\/activity\/[^/]+\/?(\?|$)/.test(req.url)) {
+        req.url = '/activity/';
+      }
+      next();
+    });
+  },
+};
+
 export default defineConfig({
   integrations: [svelte(), tailwind()],
   devToolbar: { enabled: false },
@@ -16,6 +30,7 @@ export default defineConfig({
   // When hosting at a subdirectory (e.g. GitHub Pages project site), set:
   // base: "/repo-name",
   vite: {
+    plugins: [activityFallbackPlugin],
     optimizeDeps: {
       include: ['maplibre-gl'],
       esbuildOptions: { target: 'es2022' },