feat(alarmas): replace one-line reliability button with full diagnostics screen

Surface all six DiagnosticoAlarmasAndroid fields instead of three: the
battery-optimization exemption and native pending-alarm count were
already collected but silently dropped by the old widget. Each failing
signal now offers a "Fix this" action that opens the right system
settings screen (exact alarms, notifications, full-screen intent,
battery optimization), guarded by SDK level and never crashing when a
ROM lacks that screen. Manufacturers known for aggressive background
killing (Xiaomi/Redmi/POCO, Huawei, Oppo, Vivo, OnePlus, Samsung) get
an honest explanation that Autostart must be enabled manually, since
there is no API to detect or grant it.

Notifications now deep-links straight to
ACTION_APP_NOTIFICATION_SETTINGS via a new openNotificationSettings
native method, instead of reusing the runtime permission popup meant
for first-time alarm creation.

New copy is added to all 13 ARB locales with real per-language
translations (not Spanish copies), verified by the ARB parity and
anti-copy tests plus the corruption scanner.

android/app/src/main/kotlin/es/freetimelab/pluriwave/MainActivity.kt

@@ -232,6 +232,10 @@ class MainActivity : AudioServiceActivity() {
                     Log.d(tag, "alarm.channel requestIgnoreBatteryOptimizations")
                     result.success(requestIgnoreBatteryOptimizations())
                 }
+                "openNotificationSettings" -> {
+                    Log.d(tag, "alarm.channel openNotificationSettings")
+                    result.success(openNotificationSettings())
+                }
                 "getInitialAlarmIntent" -> {
                     val payload = alarmPayload(intent)
                     Log.d(tag, "alarm.channel getInitialAlarmIntent payload=$payload")
@@ -751,6 +755,39 @@ class MainActivity : AudioServiceActivity() {
         }
     }
 
+    /**
+     * Opens the system's per-app notification settings screen directly
+     * (diagnostics screen, fix/alarmas-fiabilidad). Unlike
+     * [requestPostNotificationsPermission] -- which shows the runtime
+     * permission popup and is meant for the FIRST time an alarm is created
+     * -- this is meant for a user troubleshooting an alarm that already
+     * failed, where the OS may no longer show that popup at all after a
+     * prior denial. `ACTION_APP_NOTIFICATION_SETTINGS` only exists from API
+     * 26; older devices fall back to the app's own details screen, which
+     * still surfaces the notification toggle. Never throws across the
+     * channel boundary -- an unresolvable intent on some ROM is caught and
+     * reported as `false`, same shape as every other `request*`/`open*`
+     * helper in this class.
+     */
+    private fun openNotificationSettings(): Boolean {
+        return try {
+            val intent = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+                Intent(Settings.ACTION_APP_NOTIFICATION_SETTINGS).apply {
+                    putExtra(Settings.EXTRA_APP_PACKAGE, packageName)
+                }
+            } else {
+                Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS).apply {
+                    data = Uri.parse("package:$packageName")
+                }
+            }
+            startActivity(intent)
+            true
+        } catch (error: Throwable) {
+            Log.e(tag, "alarm.channel openNotificationSettings failed", error)
+            false
+        }
+    }
+
     private fun openDirectory(path: String): Boolean {
         val folder = File(path)
         if (!folder.exists()) {