ios: Bump min iOS version to 15.0, as required by latest Firebase iOS SDK

Firebase iOS SDK version 12.0 bumps minimum supported iOS version
to 15.0, see:
  https://firebase.google.com/support/release-notes/ios#version_1200_-_july_15_2025
  firebase/firebase-ios-sdk#14732

As we plan to bump our Firebase dependency soon, update the min iOS
version to 15.0 .

Author: rajveermalviya

ios/Flutter/AppFrameworkInfo.plist

@@ -21,6 +21,6 @@
   <key>CFBundleVersion</key>
   <string>1.0</string>
   <key>MinimumOSVersion</key>
-  <string>14.0</string>
+  <string>15.0</string>
 </dict>
 </plist>

ios/Podfile

@@ -1,7 +1,7 @@
 # This should match the iOS Deployment Target
 # (in Xcode, that's in project > Runner > Info)
 # and MinimumOSVersion in ios/Flutter/AppFrameworkInfo.plist.
-platform :ios, '14.0'
+platform :ios, '15.0'
 
 # CocoaPods analytics sends network stats synchronously affecting flutter build latency.
 ENV['COCOAPODS_DISABLE_STATS'] = 'true'

ios/Runner.xcodeproj/project.pbxproj

@@ -356,7 +356,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 14.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 15.0;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SUPPORTED_PLATFORMS = iphoneos;
@@ -435,7 +435,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 14.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 15.0;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
@@ -484,7 +484,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 14.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 15.0;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SUPPORTED_PLATFORMS = iphoneos;