feat(web): refine model availability states and preserve API key preview placeholder (#2226)

* feat(web): clarify model availability and status display

- Rename model availability field from configured to available across backend API and frontend usage

- Keep status as reason classification (configured/unconfigured/unreachable) and show unreachable in UI

- Preserve API key preview even when local service is unreachable

- Update backend tests to assert both availability and status semantics

* fix(web): clarify unreachable model status and wording

- Show unreachable status in model cards instead of API key preview when service is down

- Keep API key placeholder preview in model settings whenever an API key is already saved

- Rename model status wording from configured to available across backend, frontend, and i18n

- Update backend model status tests to match renamed status semantics

* style(web): standardize formatting in handleListModels function

* refactor(web): enforce status field as required to follow backend behavior

web/frontend/src/components/chat/chat-empty-state.tsx

@@ -10,19 +10,19 @@ import { useTranslation } from "react-i18next"
 import { Button } from "@/components/ui/button"
 
 interface ChatEmptyStateProps {
-  hasConfiguredModels: boolean
+  hasAvailableModels: boolean
   defaultModelName: string
   isConnected: boolean
 }
 
 export function ChatEmptyState({
-  hasConfiguredModels,
+  hasAvailableModels,
   defaultModelName,
   isConnected,
 }: ChatEmptyStateProps) {
   const { t } = useTranslation()
 
-  if (!hasConfiguredModels) {
+  if (!hasAvailableModels) {
     return (
       <div className="flex flex-col items-center justify-center py-20 opacity-70">
         <div className="mb-6 flex h-16 w-16 items-center justify-center rounded-2xl bg-amber-500/10 text-amber-500">

web/frontend/src/components/chat/chat-page.tsx

@@ -39,7 +39,7 @@ export function ChatPage() {
 
   const {
     defaultModelName,
-    hasConfiguredModels,
+    hasAvailableModels,
     apiKeyModels,
     oauthModels,
     localModels,
@@ -94,7 +94,7 @@ export function ChatPage() {
           hasScrolled ? "shadow-sm" : "shadow-none"
         }`}
         titleExtra={
-          hasConfiguredModels && (
+          hasAvailableModels && (
             <ModelSelector
               defaultModelName={defaultModelName}
               apiKeyModels={apiKeyModels}
@@ -140,7 +140,7 @@ export function ChatPage() {
         <div className="mx-auto flex w-full max-w-250 flex-col gap-8 pb-8">
           {messages.length === 0 && !isTyping && (
             <ChatEmptyState
-              hasConfiguredModels={hasConfiguredModels}
+              hasAvailableModels={hasAvailableModels}
               defaultModelName={defaultModelName}
               isConnected={isGatewayRunning}
             />