feat(i18n): add Chinese (zh-CN) localization for agent names (#338)

Adds Chinese (zh-CN) localization tooling: agent-names-zh.json translation map (130+ entries) and localize-agents-zh.ps1 PowerShell script for localizing agent names in Copilot agent picker.

scripts/i18n/README.md

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+# 🇨🇳 Chinese (zh-CN) Localization
+
+Localize agent `name` and `description` fields in YAML frontmatter to Simplified Chinese. This makes agent names readable in Copilot Chat's agent picker for Chinese-speaking users.
+
+## Files
+
+| File | Description |
+|------|-------------|
+| `agent-names-zh.json` | Mapping of English agent names → Chinese translations (130+ entries) |
+| `localize-agents-zh.ps1` | PowerShell script that reads the JSON and updates installed agent files |
+
+## Usage
+
+After installing agents with `install.sh --tool copilot`:
+
+```powershell
+# Localize agent names to Chinese
+powershell -ExecutionPolicy Bypass -File scripts/i18n/localize-agents-zh.ps1
+```
+
+By default, the script processes:
+- `%USERPROFILE%\.github\agents\`
+- `%USERPROFILE%\.copilot\agents\`
+
+Pass custom paths if needed:
+
+```powershell
+powershell -File scripts/i18n/localize-agents-zh.ps1 -TargetDirs @("C:\custom\path\agents")
+```
+
+## How It Works
+
+1. Reads `agent-names-zh.json` (UTF-8 encoded) for the translation map
+2. For each `.md` file in the target directories:
+   - Extracts the `name:` field from YAML frontmatter
+   - Looks up the Chinese translation
+   - Replaces `name:` and `description:` fields
+   - Writes back as UTF-8
+
+## Result
+
+Before:
+```yaml
+---
+name: Security Engineer
+description: Threat modeling, secure code review, security architecture
+---
+```
+
+After:
+```yaml
+---
+name: 安全工程师
+description: 威胁建模、安全代码审查与应用安全架构专家
+---
+```
+
+## Notes
+
+- Only modifies **installed copies** (in `~/.github/agents/`), not source files
+- Re-run after each `install.sh` update (which overwrites with English originals)
+- JSON file is the single source of truth for translations — add new agents there
+- Script is pure ASCII (avoids PowerShell encoding issues); all Chinese text lives in the JSON