feat(iap): add freemium unlock via one-time in-app purchase

Adds a permanent, non-consumable premium unlock (EstadoEntitlement +
PuertoCompras/ServicioComprasPlayBilling) that removes ads and unlocks
alarm vacations, alarms past a 5-alarm free cap, recording start, and
full Android Auto browsing. The phone equalizer stays free for everyone.

- Entitlement is prefs-backed (compra_premium_v1), fail-open, and
  resolvable headlessly via esPremiumPersistido() for the Android Auto
  audio handler, which registers before runApp.
- Android Auto reduced mode keeps the real root folder labels for free
  users; browsing into any of them (and playFromMediaId/playFromSearch/
  skipToNext/skipToPrevious) is blocked at the getChildren/servicio_audio
  choke points, with a locked "Función Premium" item as the backstop.
  Current-station play/pause/stop stays untouched. A free -> premium
  transition actively invalidates the head unit's cached browse tree.
- Ads (top banner + capped interstitial before adding a station or an
  alarm) are gated behind entitlement via ServicioAnuncios, using
  official Google test ad unit IDs pending AdMob provisioning.
- Alarm cap UX shows an explanatory message with a secondary unlock
  action rather than a bare paywall jump; existing data is grandfathered.
- 4 new localization keys translated across all 13 supported locales.

Co-located tests use strict TDD (RED test before implementation) for
every new pure-logic unit; full existing suite passes unchanged.

pubspec.lock

@@ -325,6 +325,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.3.3"
+  google_mobile_ads:
+    dependency: "direct main"
+    description:
+      name: google_mobile_ads
+      sha256: "0d4a3744b5e8ed1b8be6a1b452d309f811688855a497c6113fc4400f922db603"
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.3.1"
   hooks:
     dependency: transitive
     description:
@@ -349,6 +357,38 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.1.2"
+  in_app_purchase:
+    dependency: "direct main"
+    description:
+      name: in_app_purchase
+      sha256: "0e9510b80b0074e89ab0a8e0fc901439b779dc9ae575ab8d419253c6e1627716"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.3.0"
+  in_app_purchase_android:
+    dependency: transitive
+    description:
+      name: in_app_purchase_android
+      sha256: c04e2cad0470fc868cb0ea06477648f003220b1b6612909db83528ca83ac0905
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.5.2"
+  in_app_purchase_platform_interface:
+    dependency: transitive
+    description:
+      name: in_app_purchase_platform_interface
+      sha256: "0b0076cac8ce4fa7048f01e76af8b123aeb6a7c4e0dea2a5206d6664454f3e36"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.1"
+  in_app_purchase_storekit:
+    dependency: transitive
+    description:
+      name: in_app_purchase_storekit
+      sha256: "702a23c3d2ddc177b075d521d264900e82f01663881e4ef3ce17775de298c0e3"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.4.11"
   intl:
     dependency: "direct main"
     description:
@@ -365,6 +405,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.7.2"
+  json_annotation:
+    dependency: transitive
+    description:
+      name: json_annotation
+      sha256: "2a743920d81b7910627f68ee2c9ac1fc0bfee32b9fc3403587d7c6791ca12f80"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.12.0"
   just_audio:
     dependency: "direct main"
     description:
@@ -906,6 +954,38 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.1.1"
+  webview_flutter:
+    dependency: transitive
+    description:
+      name: webview_flutter
+      sha256: d53e1ccf5516f25017e3c9d44c39034db352d20fa34fe200674270242c2c5111
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.14.1"
+  webview_flutter_android:
+    dependency: transitive
+    description:
+      name: webview_flutter_android
+      sha256: a97db7a44f8e71af2f3971c45550a08cce1fb60059c1b8e534251e6cfb753490
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.13.0"
+  webview_flutter_platform_interface:
+    dependency: transitive
+    description:
+      name: webview_flutter_platform_interface
+      sha256: "1221c1b12f5278791042f2ec2841743784cf25c5a644e23d6680e5d718824f04"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.15.1"
+  webview_flutter_wkwebview:
+    dependency: transitive
+    description:
+      name: webview_flutter_wkwebview
+      sha256: c879dd64b87c452aa84381b244d5469da57ba7e8cca6884c7b1e0d406372c12d
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.26.0"
   win32:
     dependency: transitive
     description:
@@ -931,5 +1011,5 @@ packages:
     source: hosted
     version: "3.1.3"
 sdks:
-  dart: ">=3.10.3 <4.0.0"
-  flutter: ">=3.38.4"
+  dart: ">=3.12.0 <4.0.0"
+  flutter: ">=3.44.0"