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/mcp/McpServersScreen.kt

@@ -154,7 +154,7 @@ fun McpServersScreen(
                         SearchBar(
                             query = query,
                             onQueryChange = { query = it },
-                            placeholder = "Search MCP servers...",
+                            placeholder = stringResource(R.string.mcp_search_placeholder),
                         )
                     }
 
@@ -171,7 +171,7 @@ fun McpServersScreen(
                     } else if (filteredServers.isEmpty()) {
                         item(key = "no-match") {
                             Text(
-                                text = "No servers match \"$query\"",
+                                text = stringResource(R.string.mcp_no_match, query),
                                 style = MaterialTheme.typography.bodyMedium,
                                 color = MaterialTheme.colorScheme.onSurfaceVariant,
                                 modifier = Modifier.padding(spacing.md),