feat: add basic support for file upload via blossom (#32)

Reviewed-on: https://git.reya.su/reya/coop-mobile/pulls/32

shared/src/commonMain/kotlin/su/reya/coop/viewmodels/ChatViewModel.kt

@@ -149,7 +149,11 @@ class ChatViewModel(
         }
     }
 
-    fun sendMessage(roomId: Long, message: String, replies: List<EventId> = emptyList()) {
+    fun sendMessage(
+        roomId: Long,
+        message: String,
+        replies: List<EventId> = emptyList()
+    ) {
         if (message.isEmpty()) {
             appViewModel.showError("Message cannot be empty")
             return
@@ -173,6 +177,24 @@ class ChatViewModel(
         }
     }
 
+    suspend fun sendFileMessage(
+        roomId: Long,
+        file: ByteArray?,
+        contentType: String? = "image/jpeg",
+        replies: List<EventId> = emptyList()
+    ) {
+        if (file == null) return
+        
+        try {
+            val uri = appViewModel.blossomUpload(file, contentType)
+                ?: throw IllegalArgumentException("Failed to upload file")
+
+            sendMessage(roomId, uri, replies)
+        } catch (e: Exception) {
+            throw IllegalArgumentException("Error: ${e.message}")
+        }
+    }
+
     fun isMessageSent(id: EventId): Boolean {
         val giftWrapId = nostr.messages.rumorMap[id]
         return if (giftWrapId != null) {