feat: add image input to art/avatar modes and notes to replace mode

- Art and Avatar modes now support optional image uploads via paste or
  file picker, sent to Gemini alongside the text prompt
- Initial Replace mode gains an optional textarea for notes to include
  with the uploaded image
- Backend updated to send user images for all modes, appending replace
  instructions only when in replace mode
- Send validation updated to allow image-only messages in art/avatar

src-tauri/src/gemini.rs

@@ -83,22 +83,26 @@ fn build_user_gemini_parts(
     user_image_base64: &Option<String>,
     user_image_mime: &Option<String>,
 ) -> Vec<Value> {
-    if mode == "replace" && user_image_base64.is_some() {
+    if let Some(image_data) = user_image_base64.as_deref() {
         let mime = user_image_mime.as_deref().unwrap_or("image/png");
-        let data = user_image_base64.as_deref().unwrap_or("");
         let base_text = user_text.as_deref().unwrap_or("");
-        let final_text = if base_text.is_empty() {
+        let final_text = if mode == "replace" {
+            if base_text.is_empty() {
                 REPLACE_MODE_APPEND.to_string()
             } else {
                 format!("{}\n{}", base_text, REPLACE_MODE_APPEND)
+            }
+        } else {
+            base_text.to_string()
         };
 
-        vec![
-            json!({"inlineData": {"mimeType": mime, "data": data}}),
-            json!({"text": final_text}),
-        ]
+        let mut parts = vec![json!({"inlineData": {"mimeType": mime, "data": image_data}})];
+        if !final_text.is_empty() {
+            parts.push(json!({"text": final_text}));
+        }
+        parts
     } else {
-        // Art/avatar mode, or replace mode follow-up correction (text only)
+        // No image: text-only message
         let text = user_text.as_deref().unwrap_or("");
         vec![json!({"text": text})]
     }

src/components/inputArea.tsx

@@ -256,7 +256,8 @@ const inputArea = ({
     if (isInitialReplace && imageBase64 === undefined) {
       return;
     }
-    if (!isInitialReplace && text.trim().length === 0) {
+    const hasContent = text.trim().length > 0 || imageBase64 !== undefined;
+    if (!isInitialReplace && !hasContent) {
       return;
     }
 
@@ -332,6 +333,9 @@ const inputArea = ({
       : dropZoneInactiveClass,
   ].join(" ");
 
+  const hasNoContent = text.trim().length === 0 && imageBase64 === undefined;
+  const isSendDisabled = isLoading || hasNoContent;
+
   return (
     <div className="border-t border-purple-900/30 p-4 bg-[#0f0a1a]">
       <div className="flex items-center gap-2 mb-2">
@@ -397,6 +401,15 @@ const inputArea = ({
             type="file"
           />
 
+          <textarea
+            className={textareaClass}
+            disabled={isLoading}
+            onChange={handleTextChange}
+            placeholder="Add notes to include with the image (optional)..."
+            rows={2}
+            value={text}
+          />
+
           <button
             className={replaceButtonClass}
             disabled={isLoading || imageBase64 === undefined}
@@ -414,15 +427,16 @@ const inputArea = ({
         </div>
 
         : <div className="flex flex-col gap-3">
-          {mode === "replace"
-            ? <div className="flex flex-col gap-2">
+          <div className="flex flex-col gap-2">
             {imagePreview === undefined
               ? <button
                 className={pasteButtonClass}
                 onClick={handlePasteButtonClick}
                 type="button"
               >
-                  {"📋 Paste replacement image (optional)"}
+                {mode === "replace"
+                  ? "📋 Paste replacement image (optional)"
+                  : "📋 Paste image (optional)"}
               </button>
 
               : <div className="relative inline-block">
@@ -448,8 +462,6 @@ const inputArea = ({
             />
           </div>
 
-            : null}
-
           <div className="flex gap-3 items-end">
             <textarea
               className={textareaClass}
@@ -464,7 +476,7 @@ const inputArea = ({
             />
             <button
               className={sendButtonClass}
-              disabled={isLoading || text.trim().length === 0}
+              disabled={isSendDisabled}
               onClick={handleSend}
               type="button"
             >