feat: support old title placeholder in title prompts

app/ai.py

@@ -127,11 +127,7 @@ def gen_title(
     payload = _chat_payload(
         model,
         [
-            {"role": "system", "content": str(title_prompt or "").strip()},
-            {
-                "role": "user",
-                "content": "旧标题：\n%s\n\n请只返回新标题，不要解释。" % str(old_title or ""),
-            },
+            {"role": "user", "content": _compose_title_prompt(title_prompt, old_title)},
         ],
     )
     attempts = _attempt_count(ai_cfg, retry)
@@ -840,7 +836,7 @@ def _gen_title_cmhub(
     resolution = _normalize_cmhub_resolution(ai_cfg.get("resolution", "1k"))
     _notify_step(on_step, "title_build_request")
     payload = {
-        "prompt": _cmhub_title_prompt(title_prompt, old_title),
+        "prompt": _compose_title_prompt(title_prompt, old_title),
         "model": runtime["alias"],
         "resolution": resolution,
     }
@@ -1045,11 +1041,16 @@ def _cmhub_runtime(config, operation, cmhub_config_path):
     }
 
 
-def _cmhub_title_prompt(title_prompt, old_title):
-    return "%s\n\n旧标题：\n%s\n\n请只返回新标题，不要解释。" % (
-        str(title_prompt or "").strip(),
-        str(old_title or ""),
-    )
+def _compose_title_prompt(title_prompt, old_title):
+    prompt = str(title_prompt or "").strip()
+    old_title_text = str(old_title or "")
+    if "{旧标题}" in prompt:
+        body = prompt.replace("{旧标题}", old_title_text).strip()
+    else:
+        body = "%s\n\n旧标题：\n%s" % (prompt, old_title_text)
+    if body:
+        return "%s\n\n请只返回新标题，不要解释。" % body
+    return "请只返回新标题，不要解释。"
 
 
 def _normalize_cmhub_resolution(resolution):