Add Simplified Chinese localization

[endfish]

Summary

• Adds a Simplified Chinese (zh-CN) resource overlay for Brio's existing localization system.
• Extends the official Localize loader so English is loaded first as the fallback and an optional client-language overlay is applied afterward.
• Selects zh-CN when Dalamud reports the Simplified Chinese client language.
• Supplies Simplified Chinese translations for structured UI labels, catalog and metadata terminology, posing and camera controls, appearance options, bone names, tooltips, and menu text.

Motivation

Brio already contains the official Localize infrastructure and an embedded English language resource, but the loader currently always reads Language.en.json. This PR keeps that design and adds the smallest language-neutral extension needed for an optional embedded translation overlay.

English remains the source and fallback language. Missing Chinese keys therefore continue to display the existing English value instead of failing or producing blank labels.

Scope

• No Brio-CN assembly or manifest rename.
• No Chinese strings are hard-coded into C# source files.
• No Penumbra action-filtering or world-model-preview feature changes are included.
• The translation is isolated in Language.zh-CN.json; loader changes are language-neutral.

Validation

• Parsed Language.zh-CN.json with System.Text.Json/PowerShell JSON validation.
• dotnet build brio.slnx -c Debug
• Result: 0 warnings, 0 errors