fix(chat): show send button for attachment-only sends (#956) (#956)

The AnimatedContent gate on the composer's send button required
inputFieldValue.text.isNotBlank() in addition to canSend, so attaching an
image or file with an empty input hid the button entirely — the attachment
could never be sent on its own. ChatInputPolicy.canSend already allowed
attachment-only sends and ChatViewModel.sendMessage already accepted blank
text with pending attachments, but the button never rendered to trigger it.

Drop the stale text gate so the send affordance tracks canSend (non-empty
text OR pending attachments, plus connection). The backend handles
image-only turns natively: prompt.submit with empty text + queued images
routes through build_native_content_parts, which wraps the pixels with an
[Image attached at: ...] hint.

Add a Compose UI regression test asserting the send button is displayed
with a pending image attachment and an empty input.

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/androidTest/java/com/m57/hermescontrol/ui/chat/ChatScreenTest.kt

@@ -8,6 +8,7 @@ import androidx.compose.ui.test.performTextInput
 import androidx.core.content.ContextCompat
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.filters.MediumTest
+import com.m57.hermescontrol.data.model.Attachment
 import com.m57.hermescontrol.data.ws.ConnectionStatus
 import com.m57.hermescontrol.ui.common.ActionProgressController
 import io.mockk.every
@@ -82,4 +83,40 @@ class ChatScreenTest {
         composeTestRule.onNodeWithTag("send_button").assertIsDisplayed()
         composeTestRule.onNodeWithTag("mic_button").assertIsDisplayed()
     }
+
+    @Test
+    fun chatScreen_sendButtonShownForAttachmentWithEmptyInput() {
+        // Issue #956: an attachment queued with an EMPTY input must still show
+        // the send button — the old AnimatedContent gate required non-blank
+        // text even though ChatInputPolicy.canSend already allowed
+        // attachment-only sends.
+        val uiState =
+            ChatUiState(
+                connectionStatus = ConnectionStatus.CONNECTED,
+                pendingAttachments =
+                    listOf(
+                        Attachment(
+                            uri = "content://test/photo.jpg",
+                            name = "photo.jpg",
+                            mimeType = "image/jpeg",
+                        ),
+                    ),
+            )
+        val mockViewModel = mockk<ChatViewModel>(relaxed = true)
+        every { mockViewModel.uiState } returns MutableStateFlow(uiState).asStateFlow()
+        every { mockViewModel.streamingState } returns MutableStateFlow(StreamingState()).asStateFlow()
+        every { mockViewModel.actionProgress } returns
+            ActionProgressController(scope = CoroutineScope(Dispatchers.Main))
+
+        composeTestRule.setContent {
+            ChatScreen(
+                onOpenDrawer = {},
+                sessionId = null,
+                viewModel = mockViewModel,
+            )
+        }
+
+        composeTestRule.onNodeWithTag("chat_input").assertIsDisplayed()
+        composeTestRule.onNodeWithTag("send_button").assertIsDisplayed()
+    }
 }