feat: Add Android share target support for image sharing

Implement native Android share functionality to allow users to share
images from other apps directly to TimeSafari. This mirrors the iOS
share extension functionality and provides a seamless cross-platform
experience.

Changes:
- Add ACTION_SEND and ACTION_SEND_MULTIPLE intent filters to
  AndroidManifest.xml to register the app as a share target for images
- Implement share intent handling in MainActivity.java:
  - Process incoming share intents in onCreate() and onNewIntent()
  - Read shared image data from content URI using ContentResolver
  - Convert image to Base64 encoding
  - Write image data to temporary JSON file in app's internal storage
  - Use getFilesDir() which maps to Capacitor's Directory.Data
- Update src/main.capacitor.ts to support Android platform:
  - Extend checkAndStoreNativeSharedImage() to check for Android platform
  - Use Directory.Data for Android file operations (vs Directory.Documents for iOS)
  - Add Android to initial load and app state change listeners
  - Ensure shared image detection works on app launch and activation

The implementation follows the same pattern as iOS:
- Native layer (MainActivity) writes shared image to temp file
- JavaScript layer polls for file existence with exponential backoff
- Image is stored in temp database and user is navigated to SharedPhotoView

This enables users to share images from Gallery, Photos, and other apps
directly to TimeSafari on Android devices.

android/app/src/main/AndroidManifest.xml

@@ -27,6 +27,20 @@
                 <category android:name="android.intent.category.BROWSABLE" />
                 <data android:scheme="timesafari" />
             </intent-filter>
+
+            <!-- Share Target Intent Filter - Single Image -->
+            <intent-filter>
+                <action android:name="android.intent.action.SEND" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <data android:mimeType="image/*" />
+            </intent-filter>
+
+            <!-- Share Target Intent Filter - Multiple Images (optional, we'll handle first image) -->
+            <intent-filter>
+                <action android:name="android.intent.action.SEND_MULTIPLE" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <data android:mimeType="image/*" />
+            </intent-filter>
         </activity>
 
         <provider