fix(desktop): prevent Windows CE bootstrap encoding crash

[Luhaozhu]

Summary / 概述

Fix packaged Windows CE desktop builds exiting during the first local-server
startup after the default-plugin readiness changes from #19.

The desktop launcher redirects Python stdout and stderr to server.log. On
Windows systems where the redirected stream selected GBK, printing the ✓
status symbol raised UnicodeEncodeError inside the plugin and site-template
bootstrap try blocks. Successful work was consequently reported as failed,
and strict readiness terminated the backend before the desktop window became
usable.

This change:

• forces UTF-8 for the Python child process launched by the Tauri desktop shell;
• makes CLI status output safe on legacy code pages;
• separates status rendering from plugin and template operation results so a
  log encoding problem cannot change readiness state; and
• adds regression coverage for GBK-redirected output and the desktop launcher
  environment contract.

Related issue / 关联 Issue

Follow-up to #19.

Type of change / 变更类型

• 📖 Documentation (document/**, README*.md)
• 🧩 Example / sample (examples/**)
• 🔧 Repo meta (CI, templates, .github/**)
• Other (please describe / 请说明): Windows CE desktop startup bug fix and regressions.

Checklist / 检查项

• My change only touches non-generated paths (docs / examples / repo meta). 仅改动非生成路径。
• Links and code snippets were verified. 链接与代码片段已验证。
• For bilingual docs, I updated both document/en/** and document/zh-CN/** where applicable. 双语文档已同步更新（如适用）。
• I read CONTRIBUTING.md. 我已阅读贡献指南。

Validation:

• strict CE derivation passed required-runtime, forbidden-artifact, binary,
  brand, license, import/OpenAPI/ORM, pytest-collection, and frontend-build gates;
• 17 local bootstrap and subprocess regressions passed;
• 6 CE desktop payload tests passed;
• Black, cargo fmt, and git diff --check passed; and
• a fresh derived CE tree was launched with the installed Windows Python runtime,
  redirected logs, and UTF-8 environment overrides deliberately removed. The
  service reached /health, and the resulting log decoded as UTF-8 with the
  completed default-plugin status present.