refactor(pixel-grid): migrate reconstructor to Python

backend/packages/app/pyproject.toml

@@ -12,6 +12,8 @@ dependencies = [
     "pydantic[email]>=2.7",
     "sqlalchemy>=2.0",
     "python-multipart>=0.0.9",
+    "numpy>=1.26",
+    "pillow>=10.4",
 ]
 
 [project.scripts]

backend/packages/app/src/windup_app/server/pixel_perfect/LICENSE.pixel-art-fixer

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Astropulse, LLC
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

backend/packages/app/src/windup_app/server/pixel_perfect/UPSTREAM.md

@@ -0,0 +1,9 @@
+# Upstream
+
+两阶段重建与 deterministic k-means 逻辑源自
+[Retro-Diffusion/pixel-art-fixer](https://github.com/Retro-Diffusion/pixel-art-fixer)，
+固定于提交 `ef376e57e1c272633ca2dbf5f29ec3fcf6596465`，使用 MIT License。
+
+本目录将既有 Rust 重建器等价迁移为 NumPy/Pillow 服务端实现。迁移保留
+60,000 点确定性采样、固定种子 k-means++、Lloyd 迭代、两阶段结构投票、
+原色恢复与透明度多数票；同色点去重与规则网格缓存只减少重复计算。

backend/packages/app/src/windup_app/server/pixel_perfect/__init__.py

@@ -0,0 +1 @@
+"""独立完美像素工具的服务端算法边界。"""