refactor: migrate app.config and Expo config plugins to TypeScript

Migrate the dynamic Expo config and all 12 local config plugins from
CommonJS .js to typed TypeScript:

- app.config.js -> app.config.ts (typed ConfigContext/ExpoConfig,
  behavior-identical port)
- plugins/*.js -> plugins/*.ts with `ConfigPlugin` typings from
  expo/config-plugins; plugin options are now type-checked (withGitPod)
- app.json plugin references updated to the .ts paths
- imports unified on expo/config-plugins (some plugins used the
  @expo/config-plugins alias)

Node evaluates the config at prebuild time and cannot parse TypeScript
plugin modules on its own (verified empirically: Expo transpiles
app.config.ts itself but not its imports), so the documented tsx
approach is used: `import "tsx/cjs"` at the top of app.config.ts plus
tsx as a devDependency.

Validation: resolved prebuild configs (expo config --type prebuild) are
byte-identical to the old JS config for both mobile and TV (modulo
plugin path extensions and the builtAt timestamp); full
`bun run prebuild` and `bun run prebuild:tv` pass and all Android
plugin mods are present in the generated project (media3 exclusions,
gradle properties, cast activity, network security config, alert
colors).

plugins/withGitPod.ts

@@ -0,0 +1,32 @@
+import { type ConfigPlugin, withPodfile } from "expo/config-plugins";
+
+interface GitPodOptions {
+  podName: string;
+  podspecUrl: string;
+}
+
+const withGitPod: ConfigPlugin<GitPodOptions> = (
+  config,
+  { podName, podspecUrl },
+) => {
+  return withPodfile(config, (config) => {
+    const podfile = config.modResults.contents;
+
+    const podLine = `  pod '${podName}', :podspec => '${podspecUrl}'`;
+
+    // Check if already added
+    if (podfile.includes(podLine)) {
+      return config;
+    }
+
+    // Insert after "use_expo_modules!"
+    config.modResults.contents = podfile.replace(
+      "use_expo_modules!",
+      `use_expo_modules!\n${podLine}`,
+    );
+
+    return config;
+  });
+};
+
+export default withGitPod;