Implement complete Android app code

- Add models: Note, SyncStatus
- Add storage: NotesStorage for local file system
- Add sync: WebDavSyncService, SyncWorker, WifiSyncReceiver
- Add UI: MainActivity, NoteEditorActivity, SettingsActivity
- Add adapters: NotesAdapter
- Add utils: Constants, DeviceIdGenerator, Extensions, NotificationHelper
- Add layouts: activity_main, activity_editor, activity_settings, item_note
- Add menus and strings

android/app/src/main/java/dev/dettmer/simplenotes/MainActivity.kt

@@ -1,20 +1,160 @@
 package dev.dettmer.simplenotes
 
+import android.Manifest
+import android.content.Intent
+import android.content.pm.PackageManager
+import android.os.Build
 import android.os.Bundle
-import androidx.activity.enableEdgeToEdge
+import android.view.Menu
+import android.view.MenuItem
 import androidx.appcompat.app.AppCompatActivity
-import androidx.core.view.ViewCompat
-import androidx.core.view.WindowInsetsCompat
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+import com.google.android.material.appbar.MaterialToolbar
+import com.google.android.material.floatingactionbutton.FloatingActionButton
+import dev.dettmer.simplenotes.adapters.NotesAdapter
+import dev.dettmer.simplenotes.storage.NotesStorage
+import dev.dettmer.simplenotes.utils.NotificationHelper
+import dev.dettmer.simplenotes.utils.showToast
+import android.widget.TextView
 
 class MainActivity : AppCompatActivity() {
+    
+    private lateinit var recyclerViewNotes: RecyclerView
+    private lateinit var textViewEmpty: TextView
+    private lateinit var fabAddNote: FloatingActionButton
+    private lateinit var toolbar: MaterialToolbar
+    
+    private lateinit var adapter: NotesAdapter
+    private val storage by lazy { NotesStorage(this) }
+    
+    companion object {
+        private const val REQUEST_NOTIFICATION_PERMISSION = 1001
+    }
+    
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        enableEdgeToEdge()
         setContentView(R.layout.activity_main)
-        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)) { v, insets ->
-            val systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars())
-            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
-            insets
+        
+        // Notification Channel erstellen
+        NotificationHelper.createNotificationChannel(this)
+        
+        // Permission für Notifications (Android 13+)
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            requestNotificationPermission()
+        }
+        
+        findViews()
+        setupToolbar()
+        setupRecyclerView()
+        setupFab()
+        
+        loadNotes()
+    }
+    
+    override fun onResume() {
+        super.onResume()
+        loadNotes()
+    }
+    
+    private fun findViews() {
+        recyclerViewNotes = findViewById(R.id.recyclerViewNotes)
+        textViewEmpty = findViewById(R.id.textViewEmpty)
+        fabAddNote = findViewById(R.id.fabAddNote)
+        toolbar = findViewById(R.id.toolbar)
+    }
+    
+    private fun setupToolbar() {
+        setSupportActionBar(toolbar)
+    }
+    
+    private fun setupRecyclerView() {
+        adapter = NotesAdapter { note ->
+            openNoteEditor(note.id)
+        }
+        recyclerViewNotes.adapter = adapter
+        recyclerViewNotes.layoutManager = LinearLayoutManager(this)
+    }
+    
+    private fun setupFab() {
+        fabAddNote.setOnClickListener {
+            openNoteEditor(null)
+        }
+    }
+    
+    private fun loadNotes() {
+        val notes = storage.loadAllNotes()
+        adapter.submitList(notes)
+        
+        // Empty state
+        textViewEmpty.visibility = if (notes.isEmpty()) {
+            android.view.View.VISIBLE
+        } else {
+            android.view.View.GONE
+        }
+    }
+    
+    private fun openNoteEditor(noteId: String?) {
+        val intent = Intent(this, NoteEditorActivity::class.java)
+        noteId?.let {
+            intent.putExtra(NoteEditorActivity.EXTRA_NOTE_ID, it)
+        }
+        startActivity(intent)
+    }
+    
+    private fun openSettings() {
+        startActivity(Intent(this, SettingsActivity::class.java))
+    }
+    
+    override fun onCreateOptionsMenu(menu: Menu): Boolean {
+        menuInflater.inflate(R.menu.menu_main, menu)
+        return true
+    }
+    
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        return when (item.itemId) {
+            R.id.action_settings -> {
+                openSettings()
+                true
+            }
+            R.id.action_sync -> {
+                // Manual sync trigger could be added here
+                showToast("Sync wird in den Einstellungen gestartet")
+                true
+            }
+            else -> super.onOptionsItemSelected(item)
+        }
+    }
+    
+    private fun requestNotificationPermission() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            if (checkSelfPermission(Manifest.permission.POST_NOTIFICATIONS) 
+                != PackageManager.PERMISSION_GRANTED) {
+                requestPermissions(
+                    arrayOf(Manifest.permission.POST_NOTIFICATIONS),
+                    REQUEST_NOTIFICATION_PERMISSION
+                )
+            }
+        }
+    }
+    
+    override fun onRequestPermissionsResult(
+        requestCode: Int,
+        permissions: Array<out String>,
+        grantResults: IntArray
+    ) {
+        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
+        
+        when (requestCode) {
+            REQUEST_NOTIFICATION_PERMISSION -> {
+                if (grantResults.isNotEmpty() && 
+                    grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+                    showToast("Benachrichtigungen aktiviert")
+                } else {
+                    showToast("Benachrichtigungen deaktiviert. " +
+                        "Du kannst sie in den Einstellungen aktivieren.")
+                }
+            }
         }
     }
 }