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/test/java/com/m57/hermescontrol/ui/system/SystemViewModelTest.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.ui.system
 
+import android.app.Application
+import io.mockk.mockk
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.test.StandardTestDispatcher
@@ -14,6 +16,7 @@ import org.junit.Test
 @OptIn(ExperimentalCoroutinesApi::class)
 class SystemViewModelTest {
     private val testDispatcher = StandardTestDispatcher()
+    private val mockApp = mockk<Application>(relaxed = true)
 
     @Before
     fun setup() {
@@ -27,7 +30,7 @@ class SystemViewModelTest {
 
     @Test
     fun `openUpdateConfirm sets updateConfirmOpen to true`() {
-        val viewModel = SystemViewModel()
+        val viewModel = SystemViewModel(mockApp)
 
         assertFalse(viewModel.uiState.value.updateConfirmOpen)
 
@@ -38,7 +41,7 @@ class SystemViewModelTest {
 
     @Test
     fun `closeUpdateConfirm sets updateConfirmOpen to false`() {
-        val viewModel = SystemViewModel()
+        val viewModel = SystemViewModel(mockApp)
 
         // First open it
         viewModel.openUpdateConfirm()