fix: address community review — system default, clearable schema flag, UTC fallback

- Add 'System default' clear option to SearchableSelect via clearLabel prop
- Add clearable flag to ConfigFieldSchema (schema-driven, not hardcoded)
- Add clearable: true to timezone schema override in web_server.py
- Fix CommandItem value for clear item: use clearLabel instead of '' so
  cmdk can match it during search
- Fix backend: or ['UTC'] fallback for hosts without tzdata where
  available_timezones() returns an empty set (not an exception)
- Add systemDefault i18n key (en, types, zh)

apps/desktop/src/app/settings/config-field.tsx

@@ -101,6 +101,7 @@ export function ConfigField({
   if (selectOptions && schema.searchable) {
     return row(
       <SearchableSelect
+        clearLabel={schema.clearable ? c.systemDefault : undefined}
         emptyMessage={c.noResults}
         onChange={next => onChange(next)}
         options={selectOptions.filter(o => o !== '')}

apps/desktop/src/app/settings/searchable-select.tsx

@@ -21,13 +21,17 @@ export function SearchableSelect({
   onChange,
   options,
   placeholder = 'Search…',
-  emptyMessage = 'No results found.'
+  emptyMessage = 'No results found.',
+  clearLabel
 }: {
   value: string
   onChange: (value: string) => void
   options: string[]
   placeholder?: string
   emptyMessage?: string
+  /** When set, prepends a "clear" item that sets the value to ''.
+   *  Matches the existing <Select> pattern of EMPTY_SELECT_VALUE + "(none)". */
+  clearLabel?: string
 }) {
   const [open, setOpen] = useState(false)
   const triggerRef = useRef<HTMLButtonElement>(null)
@@ -85,6 +89,18 @@ export function SearchableSelect({
           <CommandList>
             <CommandEmpty>{emptyMessage}</CommandEmpty>
             <CommandGroup>
+              {clearLabel && (
+                <CommandItem
+                  onSelect={() => handleSelect('')}
+                  value={clearLabel}
+                >
+                  <Codicon
+                    className={cn('mr-2 size-4', value === '' ? 'opacity-100' : 'opacity-0')}
+                    name="check"
+                  />
+                  {clearLabel}
+                </CommandItem>
+              )}
               {options.map(option => (
                 <CommandItem
                   key={option}

apps/desktop/src/i18n/en.ts

@@ -540,6 +540,7 @@ export const en: Translations = {
       commaSeparated: 'comma-separated values',
       searchPlaceholder: 'Search…',
       noResults: 'No results found',
+      systemDefault: 'System default',
       loading: 'Loading Hermes configuration...',
       emptyTitle: 'Nothing to configure',
       emptyDesc: 'This section has no adjustable settings.',

apps/desktop/src/i18n/types.ts

@@ -447,6 +447,7 @@ export interface Translations {
       commaSeparated: string
       searchPlaceholder: string
       noResults: string
+      systemDefault: string
       loading: string
       emptyTitle: string
       emptyDesc: string

apps/desktop/src/i18n/zh.ts

@@ -750,6 +750,7 @@ export const zh: Translations = {
       commaSeparated: '逗号分隔的值',
       searchPlaceholder: '搜索…',
       noResults: '未找到结果',
+      systemDefault: '系统默认',
       loading: '正在加载 Hermes 配置...',
       emptyTitle: '无可配置项',
       emptyDesc: '此分区没有可调整的设置。',

apps/desktop/src/types/hermes.ts

@@ -5,6 +5,9 @@ export interface ConfigFieldSchema {
   /** When true, renders a SearchableSelect (Popover + cmdk) instead of the
    *  closed `<Select>` dropdown. For large option lists like IANA timezones. */
   searchable?: boolean
+  /** When true, a searchable select prepends a "clear" item that resets the
+   *  value to ''. Matches the existing <Select> EMPTY_SELECT_VALUE pattern. */
+  clearable?: boolean
   type?: 'boolean' | 'list' | 'number' | 'select' | 'string' | 'text'
 }
 

hermes_cli/web_server.py

@@ -803,7 +803,7 @@ def _timezone_options() -> List[str]:
     """Return sorted IANA timezone identifiers, cached at import time."""
     try:
         import zoneinfo
-        return sorted(zoneinfo.available_timezones())
+        return sorted(zoneinfo.available_timezones()) or ["UTC"]
     except Exception:  # pragma: no cover
         return ["UTC"]
 
@@ -814,6 +814,7 @@ _SCHEMA_OVERRIDES: Dict[str, Dict[str, Any]] = {
         "description": "IANA timezone (e.g. America/New_York). Blank uses the system timezone.",
         "options": _timezone_options(),
         "searchable": True,
+        "clearable": True,
     },
     "memory.provider": {
         "type": "select",