add prune database function

shared/src/commonMain/kotlin/su/reya/coop/Nostr.kt

@@ -188,6 +188,14 @@ class Nostr {
         }
     }
 
+    suspend fun prune() {
+        try {
+            client?.database()?.wipe()
+        } catch (e: Exception) {
+            throw IllegalStateException("Failed to prune database: ${e.message}", e)
+        }
+    }
+
     suspend fun setSigner(new: AsyncNostrSigner) {
         try {
             signer.switch(new)

shared/src/commonMain/kotlin/su/reya/coop/NostrViewModel.kt

@@ -325,8 +325,11 @@ class NostrViewModel(
 
     fun logout() {
         viewModelScope.launch {
-            secretStore.clear("user_signer")
+            // Reset the nostr state and wipe database
             nostr.signer.switch(Keys.generate())
+            nostr.prune()
+            // Clear credential
+            secretStore.clear("user_signer")
             _signerRequired.value = true
         }
     }