feat(tracker): add FIFO prompt queue for batch image linking (#52)

Batch workflows encode all prompts first, then save all images later.
The queue preserves encode order so each image links to the correct
prompt by position (pop on save matches push on encode).

utils/prompt_tracker.py

@@ -76,6 +76,10 @@ class PromptTracker:
         self._local = threading.local()
         self.active_prompts = {}  # Global tracking for multiple threads
         self.lock = threading.Lock()
+        # FIFO queue for batch workflows: prompt_ids are pushed during encoding
+        # and popped during image linking, preserving correct ordering.
+        self._prompt_queue = []
+        self._queue_lock = threading.Lock()
 
         # Read from GalleryConfig if available, otherwise use defaults
         try:
@@ -159,6 +163,13 @@ class PromptTracker:
         with self.lock:
             self.active_prompts[execution_id] = execution_context
 
+        # Push to batch queue for ordered image linking
+        with self._queue_lock:
+            self._prompt_queue.append(execution_context)
+            self.logger.debug(
+                f"Queue size: {len(self._prompt_queue)} after push for prompt {prompt_id}"
+            )
+
         self.logger.debug(
             f"Set current prompt: {execution_id} -> {prompt_text[:50]}... (thread: {threading.current_thread().ident})"
         )
@@ -207,6 +218,26 @@ class PromptTracker:
         )
         return None
 
+    def pop_next_prompt(self) -> Optional[Dict[str, Any]]:
+        """Pop the next prompt from the batch queue (FIFO).
+
+        In batch workflows, prompts are encoded in order and images are saved
+        in the same order. This method pops the oldest queued prompt, ensuring
+        each image links to the correct prompt by position.
+
+        Returns:
+            Prompt context dict, or None if queue is empty
+        """
+        with self._queue_lock:
+            if self._prompt_queue:
+                ctx = self._prompt_queue.pop(0)
+                self.logger.debug(
+                    f"Queue pop: prompt {ctx.get('id')} "
+                    f"({len(self._prompt_queue)} remaining)"
+                )
+                return ctx
+        return None
+
     def _find_recent_prompt(self) -> Optional[Dict[str, Any]]:
         """Find the most recent prompt that's still valid.