docs: document zh-Hans locale activation for issue #566

- Add locale option to config.example.toml [tui] section with all
  supported values (auto/en/ja/zh-Hans/pt-BR) and clear notes that
  this controls TUI chrome only, not model output language.
- Fix README.zh-CN.md: settings.toml → config.toml (wrong filename).
- Expand README.zh-CN.md locale section with concrete config snippet
  and LANG= env-var example; add link to docs/LOCALIZATION.md.

The zh-Hans locale has been fully implemented in localization.rs since
v0.7.6 — this commit makes it discoverable without reading source code.

Closes #566

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config.example.toml

@@ -196,6 +196,11 @@ alternate_screen = "auto"   # auto | always | never
 mouse_capture = true        # true copies only transcript user/assistant text; false uses raw terminal selection/copy
 terminal_probe_timeout_ms = 500 # optional startup terminal-mode timeout (100-5000ms)
 osc8_links = true            # emit OSC 8 escapes around URLs (Cmd+click in iTerm2/Ghostty/Kitty/WezTerm/Terminal.app 13+); set false for terminals that misrender
+# locale = "auto"           # UI chrome language: auto | en | ja | zh-Hans | pt-BR
+#                           # "auto" reads LC_ALL → LC_MESSAGES → LANG; falls back to English.
+#                           # Override: `locale = "zh-Hans"` for Simplified Chinese regardless of OS locale.
+#                           # Also settable at runtime: /config locale zh-Hans
+#                           # Note: this only affects TUI labels/chrome — it does NOT change model output language.
 
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