feat(cherry-tomato): 新增图片混淆/解混淆插件（小番茄）

Gilbert 曲线像素重排，可与网页版互解；`混淆` / `解混淆` 命令
（回复图片或图文同条消息发送），附 tests/test_cherry_tomato.py

Co-Authored-By: Claude Code <noreply@anthropic.com>

hexi/plugins/nonebot_plugin_cherry_tomato/handlers/__init__.py

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+"""小番茄图片混淆 —— Trigger 层。"""
+
+from .obfuscate import deobf_cmd, obf_cmd  # noqa: F401

hexi/plugins/nonebot_plugin_cherry_tomato/handlers/obfuscate.py

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+"""混淆/解混淆 —— 触发器（Trigger）层。
+
+回复一张图片后发「混淆」或「解混淆」触发（图片与命令同一条消息直接发也行，
+不需要 @bot）；下载图片 → 变换 → 结果图发回。算法层见 utils/obfuscation.py。
+"""
+
+from __future__ import annotations
+
+import re
+
+from nonebot import on_command
+from nonebot.adapters.onebot.v11 import Bot, MessageEvent
+from nonebot.log import logger
+from nonebot_plugin_alconna import UniMessage
+
+from hexi.core.cooldown import cooldown
+from hexi.core.message_utils import get_reply_message
+
+from .. import config
+from ..services.pipeline import download_image, run_pipeline
+
+# 两个命令共用同一冷却器（name 相同）：同一用户 10 秒内不能连发混淆/解混淆
+obf_cmd = cooldown(10, hint="处理太频繁了，{secs} 秒后再试", name="cherry_tomato")(
+    on_command("混淆", aliases={"小番茄混淆"}, priority=10, block=True)
+)
+deobf_cmd = cooldown(10, hint="处理太频繁了，{secs} 秒后再试", name="cherry_tomato")(
+    on_command("解混淆", aliases={"小番茄解混淆"}, priority=10, block=True)
+)
+
+_MD5_RE = re.compile(r"[0-9A-Fa-f]{32}")
+
+
+@obf_cmd.handle()
+async def _obfuscate(event: MessageEvent, bot: Bot) -> None:
+    await _handle(event, bot, decrypt=False)
+
+
+@deobf_cmd.handle()
+async def _deobfuscate(event: MessageEvent, bot: Bot) -> None:
+    await _handle(event, bot, decrypt=True)
+
+
+async def _extract_image(
+    event: MessageEvent, bot: Bot
+) -> tuple[str | None, str | None]:
+    """取被回复（或当前）消息里第一张图的 (url, file)。
+
+    优先段里的 url；没有 url 时用 file 调 OneBot get_image 现换一个。
+    file 仅用于 offpic 链接失效时的 md5 兜底重试。
+    """
+    for seg in get_reply_message(event):
+        if seg.type != "image":
+            continue
+        data = seg.data or {}
+        url = data.get("url")
+        if url:
+            return str(url), str(data.get("file") or "")
+        file = data.get("file")
+        if not file:
+            continue
+        try:
+            info = await bot.get_image(file=str(file))
+        except Exception as e:  # noqa: BLE001
+            logger.warning(f"cherry_tomato: get_image 取 url 失败: {e!r}")
+            continue
+        url = info.get("url") if isinstance(info, dict) else None
+        if url:
+            return str(url), str(file)
+    return None, None
+
+
+def _offpic_md5(url: str, file: str | None) -> str | None:
+    """从 file 字段或 offpic 链接里找 32 位十六进制（md5）串；找不到返回 None。"""
+    for candidate in (file, url):
+        match = _MD5_RE.search(candidate or "")
+        if match:
+            return match.group(0).upper()
+    return None
+
+
+async def _download_with_fallback(url: str, file: str | None) -> bytes | None:
+    """下载图片；offpic 老链接失败时用 md5 换 gchat 链接重试一次（picfinder 先例）。"""
+    data = await download_image(url)
+    if data is not None:
+        return data
+    if "c2cpicdw.qpic.cn/offpic_new/" in url:
+        md5 = _offpic_md5(url, file)
+        if md5:
+            retry_url = f"http://gchat.qpic.cn/gchatpic_new/0/0-0-{md5}/0?term=2"
+            logger.info("cherry_tomato: offpic 原链下载失败，改用 gchat 链接重试")
+            data = await download_image(retry_url)
+    return data
+
+
+async def _handle(event: MessageEvent, bot: Bot, *, decrypt: bool) -> None:
+    action = "解混淆" if decrypt else "混淆"
+
+    url, file = await _extract_image(event, bot)
+    if not url:
+        await UniMessage.text(
+            "请回复一张图片再发这个命令，或把图片和命令一起发~"
+        ).finish()
+
+    data = await _download_with_fallback(url, file)
+    if data is None:
+        logger.warning(f"cherry_tomato: 图片下载失败 url={url}")
+        await UniMessage.text("图片下载失败，可能链接已过期，重发一次试试").finish()
+
+    logger.info(f"cherry_tomato: {action}开始 user={event.get_user_id()} url={url}")
+    max_pixels = config.decrypt_max_pixels() if decrypt else config.max_pixels()
+    out, err, notes = await run_pipeline(
+        data, decrypt=decrypt, max_pixels=max_pixels, quality=config.jpeg_quality()
+    )
+    if out is None:
+        logger.warning(f"cherry_tomato: {action}失败: {err}")
+        await UniMessage.text(err or f"{action}失败了，换一张图试试").finish()
+
+    image = UniMessage.image(raw=out)
+    if notes:
+        await (UniMessage.text("；".join(notes) + "\n") + image).send()
+    else:
+        await image.send()