feat: Add iOS Notification Service Extension for localizable push notifications

ios/Notification Service Extension/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>NSExtension</key>
+	<dict>
+		<key>NSExtensionPointIdentifier</key>
+		<string>com.apple.usernotifications.service</string>
+		<key>NSExtensionPrincipalClass</key>
+		<string>$(PRODUCT_MODULE_NAME).NotificationService</string>
+	</dict>
+</dict>
+</plist>

ios/Notification Service Extension/Notification Service Extension.entitlements

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>com.apple.security.application-groups</key>
+	<array>
+		<string>group.im.fluffychat.app</string>
+	</array>
+</dict>
+</plist>

ios/Notification Service Extension/NotificationService.swift

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+//
+//  NotificationService.swift
+//  Notification Extension
+//
+//  Created by Christian Pauly on 26.08.25.
+//
+
+import UserNotifications
+import os
+
+class NotificationService: UNNotificationServiceExtension {
+
+    var contentHandler: ((UNNotificationContent) -> Void)?
+    var bestAttemptContent: UNMutableNotificationContent?
+
+    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
+        self.contentHandler = contentHandler
+        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
+        
+        if let bestAttemptContent = bestAttemptContent {
+            // Uncomment to read the push message payload:
+            // os_log("[FluffyChatPushHelper] New message received: %{public}@", log: .default, type: .error, bestAttemptContent.userInfo)
+            os_log("[FluffyChatPushHelper] New message received")
+            
+            guard let roomId = bestAttemptContent.userInfo["room_id"] as? String,
+                  let eventId = bestAttemptContent.userInfo["event_id"] as? String else {
+                os_log("[FluffyChatPushHelper] Room ID or Event ID is missing!")
+                let emptyContent = UNMutableNotificationContent()
+                contentHandler(emptyContent)
+                return
+            }
+            bestAttemptContent.threadIdentifier = roomId
+            
+            if
+               let jsonString = bestAttemptContent.userInfo["counts"] as? String,
+               let jsonData = jsonString.data(using: .utf8),
+               let jsonMap = try? JSONSerialization.jsonObject(with: jsonData, options: []) as? [String: Any],
+               let unread = jsonMap["unread"] as? Int {
+                bestAttemptContent.title = String(
+                    localized: "\(unread) unread messages",
+                    comment: "Default notification title"
+                )
+                bestAttemptContent.badge = NSNumber(integerLiteral: unread)
+            }
+            
+            // TODO: Download and decrypt event to display a better body:
+            bestAttemptContent.body = String(
+                localized: "New message - open app to read",
+                comment: "Default notification body"
+            )
+            
+            contentHandler(bestAttemptContent)
+        }
+    }
+    
+    override func serviceExtensionTimeWillExpire() {
+        // Called just before the extension will be terminated by the system.
+        // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
+        if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
+            contentHandler(bestAttemptContent)
+        }
+    }
+}