fix: Android initialization bug and iOS 14 availability annotations

- Fix Android PlatformException on first run after initialize (fixes #645)
  - Update currentDispatcherHandle when initialize() is called
  - Add validation for callback handle
- Add iOS 14.0 availability annotation to LoggingDebugHandler (fixes #641)
  - Prevents build errors when os.Logger is used
- Update documentation with iOS 14.0 minimum deployment target requirement (fixes #639)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ened

docs/quickstart.mdx

@@ -23,6 +23,15 @@ flutter pub get
 Android works automatically - no additional setup required! ✅
 
 ### iOS
+
+<Warning>
+**iOS Minimum Deployment Target:** iOS 14.0 or later is required. Update your project's deployment target in Xcode:
+1. Open `ios/Runner.xcodeproj` in Xcode
+2. Select the Runner target
+3. Set "Minimum Deployments" to iOS 14.0 or later
+4. Or edit `ios/Runner.xcodeproj/project.pbxproj` and set `IPHONEOS_DEPLOYMENT_TARGET = 14.0;`
+</Warning>
+
 iOS requires a 5-minute setup in Xcode. Choose your approach based on your needs:
 
 #### Option A: Periodic Tasks (Recommended for most use cases)

workmanager_android/android/src/main/kotlin/dev/fluttercommunity/workmanager/WorkmanagerPlugin.kt

@@ -47,7 +47,20 @@ class WorkmanagerPlugin :
         callback: (Result<Unit>) -> Unit,
     ) {
         try {
-            preferenceManager.saveCallbackDispatcherHandleKey(request.callbackHandle)
+            val handle = request.callbackHandle
+
+            // Validate the handle
+            if (handle <= 0L) {
+                callback(Result.failure(Exception("Invalid callback handle provided to initialize")))
+                return
+            }
+
+            // Save to SharedPreferences
+            preferenceManager.saveCallbackDispatcherHandleKey(handle)
+
+            // Update the local variable to match
+            currentDispatcherHandle = handle
+
             callback(Result.success(Unit))
         } catch (e: Exception) {
             callback(Result.failure(e))

workmanager_apple/ios/Sources/workmanager_apple/LoggingDebugHandler.swift

@@ -3,7 +3,9 @@ import os
 
 /**
  * A debug handler that outputs debug information to iOS's unified logging system.
+ * Note: This class requires iOS 14.0 or later due to the use of os.Logger.
  */
+@available(iOS 14.0, *)
 public class LoggingDebugHandler: WorkmanagerDebug {
     private let logger = os.Logger(subsystem: "dev.fluttercommunity.workmanager", category: "debug")