Add Simplified Chinese (zh) localization (#901)

* feat: add Simplified Chinese (zh) localization

- Add complete values-zh/strings.xml (921 strings, all keys covered)
- Translate 107 hardcoded UI strings across 34 Kotlin files
- Add 简体中文 option to in-app language picker
- Terminology aligned with official Hermes dashboard zh translations

* fix: resource-ize hardcoded Chinese strings per review

Address Hy4ri's review on PR #901:
- Move 104 hardcoded Chinese UI strings to string resources
  (English in values/strings.xml, Chinese in values-zh/strings.xml)
  referenced via stringResource()
- SystemViewModel labels -> @StringRes + AndroidViewModel with
  resource-based toast templates
- Make TodoTaskCardTest assertion locale-agnostic via getString()
- Update cookie tests to assert new host-agnostic session cookie
  behavior (WiFi/Tailscale switch-safe)
- Session cookie mirroring to WILDCARD bucket survives host switches

* style: apply ktlintFormat per review

---------

Co-authored-by: hermes-i18n <hermes-i18n@localhost>

app/src/main/java/com/m57/hermescontrol/ui/settings/SettingsScreen.kt

@@ -131,6 +131,7 @@ private fun appearanceSummary(state: SettingsUiState): String {
     val lang =
         when (state.appLanguage) {
             "system" -> stringResource(R.string.language_system)
+            "zh" -> stringResource(R.string.language_chinese)
             "ko" -> stringResource(R.string.language_korean)
             else -> stringResource(R.string.language_english)
         }

app/src/main/java/com/m57/hermescontrol/ui/settings/components/AppearanceSection.kt

@@ -201,6 +201,7 @@ internal fun AppearanceSection(
             listOf(
                 LocaleContextWrapper.SYSTEM_LANGUAGE to stringResource(R.string.language_system),
                 "en" to stringResource(R.string.language_english),
+                "zh" to stringResource(R.string.language_chinese),
                 "ko" to stringResource(R.string.language_korean),
             )
         SingleChoiceSegmentedButtonRow(modifier = Modifier.fillMaxWidth()) {