feat(settings): move language to its own section with scalable dropdown picker (#906)

- New Language row in the main Settings list with current-language summary
- New SettingsLanguage drill-down page with an OutlinedButton + DropdownMenu
  picker (scales to any number of languages; same pattern as theme presets)
- Shared supportedLanguages()/languageLabel() helpers — adding a language
  is now one entry in one place
- Removed the 4-option segmented pill row from the Appearance page
- Added settings_sec_language string (en + zh)

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/res/values/strings.xml

@@ -169,6 +169,7 @@
     <string name="settings_delay_100ms">100 ms</string>
     <string name="settings_action_test_connection">Test Connection</string>
     <string name="settings_sec_about">About</string>
+    <string name="settings_sec_language">Language</string>
     <string name="settings_about_app_name">Hermes Mobile</string>
     <string name="settings_about_version">Version</string>
     <string name="settings_about_build">Build</string>