feat: 完成T-302p提示词管理

新增app/prompts.py，支持标题提示词读写、封面模板列表/读取/保存/重命名/删除，以及旧标题、新标题、商品id、店铺变量替换。

Tab②接入标题提示词启动回显和保存，封面模板下拉、新建、保存、另存为、重命名、删除、插入{新标题}与变量预览；本任务仍不调用AI、不写SQLite。

新增tests/test_prompts.py并扩展GUI测试覆盖提示词文件管理和预览；同步任务看板、API、routes、current-state和progress，下一个任务更新为T-303。

app/prompts.py

@@ -0,0 +1,133 @@
+"""Prompt file management and variable rendering."""
+
+from __future__ import annotations
+
+import os
+
+
+TITLE_PROMPT_PATH = "title_prompt.txt"
+COVER_PROMPTS_DIR = os.path.join("prompts", "cover")
+TEMPLATE_EXT = ".txt"
+INVALID_NAME_CHARS = set('\\/:*?"<>|')
+
+
+class PromptError(RuntimeError):
+    """Raised when prompt files or template names are invalid."""
+
+
+def load_title_prompt(path=TITLE_PROMPT_PATH) -> str:
+    """Load the title prompt text. Missing file means an empty prompt."""
+
+    if not os.path.exists(path):
+        return ""
+    with open(path, "r", encoding="utf-8") as fh:
+        return fh.read()
+
+
+def save_title_prompt(text, path=TITLE_PROMPT_PATH) -> None:
+    """Save the title prompt text as UTF-8."""
+
+    directory = os.path.dirname(os.path.abspath(path))
+    if directory:
+        os.makedirs(directory, exist_ok=True)
+    with open(path, "w", encoding="utf-8") as fh:
+        fh.write(str(text or ""))
+
+
+def list_cover_templates(directory=COVER_PROMPTS_DIR):
+    """Return cover template names sorted by display name."""
+
+    if not os.path.isdir(directory):
+        return []
+    names = []
+    for filename in os.listdir(directory):
+        if filename.lower().endswith(TEMPLATE_EXT):
+            names.append(filename[: -len(TEMPLATE_EXT)])
+    return sorted(names, key=str.casefold)
+
+
+def load_cover_template(name, directory=COVER_PROMPTS_DIR) -> str:
+    """Load one cover prompt template."""
+
+    path = _template_path(name, directory)
+    if not os.path.exists(path):
+        raise PromptError(f"封面提示词模板不存在: {_normalize_name(name)}")
+    with open(path, "r", encoding="utf-8") as fh:
+        return fh.read()
+
+
+def save_cover_template(name, text, directory=COVER_PROMPTS_DIR) -> None:
+    """Save one cover prompt template as UTF-8."""
+
+    path = _template_path(name, directory)
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "w", encoding="utf-8") as fh:
+        fh.write(str(text or ""))
+
+
+def rename_cover_template(old, new, directory=COVER_PROMPTS_DIR) -> None:
+    """Rename a cover prompt template with duplicate-name protection."""
+
+    old_path = _template_path(old, directory)
+    new_path = _template_path(new, directory)
+    if not os.path.exists(old_path):
+        raise PromptError(f"封面提示词模板不存在: {_normalize_name(old)}")
+    if os.path.exists(new_path):
+        raise PromptError(f"封面提示词模板已存在: {_normalize_name(new)}")
+    os.makedirs(os.path.dirname(new_path), exist_ok=True)
+    os.replace(old_path, new_path)
+
+
+def delete_cover_template(name, directory=COVER_PROMPTS_DIR) -> None:
+    """Delete one cover prompt template."""
+
+    path = _template_path(name, directory)
+    if not os.path.exists(path):
+        raise PromptError(f"封面提示词模板不存在: {_normalize_name(name)}")
+    os.remove(path)
+
+
+def render_prompt(template_text, task) -> str:
+    """Render known task variables in a prompt template."""
+
+    values = {
+        "旧标题": _task_value(task, "old_title", "旧标题"),
+        "新标题": _task_value(task, "new_title", "新标题"),
+        "商品id": _task_value(task, "item_id", "商品id", "商品ID"),
+        "店铺": _task_value(task, "shop", "account_name", "店铺", "alias"),
+    }
+    rendered = str(template_text or "")
+    for name, value in values.items():
+        rendered = rendered.replace("{" + name + "}", value)
+    return rendered
+
+
+def _task_value(task, *names) -> str:
+    for name in names:
+        value = None
+        if isinstance(task, dict):
+            value = task.get(name)
+        else:
+            value = getattr(task, name, None)
+        if value is not None:
+            return str(value)
+    return ""
+
+
+def _template_path(name, directory) -> str:
+    normalized = _normalize_name(name)
+    return os.path.abspath(os.path.join(directory, normalized + TEMPLATE_EXT))
+
+
+def _normalize_name(name) -> str:
+    value = str(name or "").strip()
+    if value.lower().endswith(TEMPLATE_EXT):
+        value = value[: -len(TEMPLATE_EXT)]
+    value = value.strip()
+    if not value:
+        raise PromptError("封面提示词模板名不能为空")
+    if value in {".", ".."} or any(char in INVALID_NAME_CHARS for char in value):
+        raise PromptError(f"封面提示词模板名非法: {value}")
+    if os.path.basename(value) != value:
+        raise PromptError(f"封面提示词模板名非法: {value}")
+    return value