fix(agent): minimal safety net, zero-config router, LLM provider status UI

- Remove deterministic intent matching (keyword lists, infer_tool,
  fast_confirmation, negation guard, classification sets)
- Embedding descriptions auto-generated from tool docstrings
- LLM provider health endpoint GET /api/agent/llm-status
- 3 error codes: LLM_PROVIDER_UNAVAILABLE, LLM_TIMEOUT, LLM_AUTH_ERROR
- Frontend banner with auto-retry 30s + input disable
- i18n for LLM status messages (assistant.json ru/en)
- 138 passing backend tests

frontend/src/lib/components/agent/AgentChat.svelte

@@ -736,7 +736,7 @@
               aria-label={$t.assistant?.input_placeholder || "Введите команду..."}
               bind:value={inputText}
               rows="1"
-              placeholder={llmInputBlocked ? (model.llmBannerMessage || "LLM недоступен...") : ($t.assistant?.input_placeholder || "Введите команду...")}
+              placeholder={llmInputBlocked ? (model.llmBannerMessage || $t.assistant?.llm_placeholder || "LLM недоступен...") : ($t.assistant?.input_placeholder || "Введите команду...")}
               class="min-h-[44px] max-h-[120px] w-full resize-none rounded-xl border border-border-strong bg-surface-page px-4 py-3 pr-12 text-sm text-text outline-none transition placeholder:text-text-subtle focus:border-primary-ring focus:ring-2 focus:ring-primary-light disabled:cursor-not-allowed disabled:opacity-50"
               onkeydown={handleKeydown}
               disabled={isInputLocked}

frontend/src/lib/components/agent/LlmStatusBanner.svelte

@@ -9,6 +9,8 @@
 <!-- @UX_FEEDBACK Toast when status changes from unavailable to ok -->
 <!-- @UX_RECOVERY Retry button, Dismiss (×) button -->
 <script lang="ts">
+  import { t } from "$lib/i18n/index.svelte.js";
+
   let {
     status,
     message,
@@ -53,7 +55,7 @@
     <p class="text-sm font-medium text-text">{message}</p>
     {#if retryCountdown > 0 && status !== "auth_error"}
       <p class="text-xs text-text-muted mt-1">
-        Auto-retry через {retryCountdown}с…
+        {t.assistant?.llm_auto_retry_countdown?.replace("{seconds}", String(retryCountdown)) || `Auto-retry через ${retryCountdown}с…`}
       </p>
     {/if}
   </div>
@@ -63,13 +65,13 @@
         class="text-xs font-medium px-3 py-1.5 rounded-md bg-primary text-white hover:bg-primary-hover transition-colors"
         onclick={onRetry}
       >
-        Retry now
+        {t.assistant?.llm_retry_now || "Retry now"}
       </button>
     {/if}
     <button
       class="text-text-muted hover:text-text transition-colors text-lg leading-none px-1"
       onclick={onDismiss}
-      aria-label="Dismiss"
+      aria-label={t.assistant?.llm_dismiss || "Dismiss"}
     >
       ×
     </button>

frontend/src/lib/i18n/locales/en/assistant.json

@@ -120,5 +120,13 @@
   "indicator_complete": "Completed",
   "time_just_now": "just now",
   "time_min": "m",
-  "time_hr": "h"
+  "time_hr": "h",
+  "llm_unavailable": "LLM provider unavailable. Check upstream API connection.",
+  "llm_timeout": "LLM provider not responding. Connection timeout.",
+  "llm_auth_error": "LLM API key rejected. Check credentials.",
+  "llm_unknown_status": "LLM status unknown.",
+  "llm_auto_retry_countdown": "Auto-retry in {seconds}s…",
+  "llm_retry_now": "Retry now",
+  "llm_placeholder": "LLM unavailable...",
+  "llm_dismiss": "Dismiss"
 }

frontend/src/lib/i18n/locales/ru/assistant.json

@@ -120,5 +120,13 @@
   "indicator_complete": "Завершён",
   "time_just_now": "только что",
   "time_min": "мин",
-  "time_hr": "ч"
+  "time_hr": "ч",
+  "llm_unavailable": "LLM провайдер недоступен. Проверьте подключение к upstream API.",
+  "llm_timeout": "LLM провайдер не отвечает. Таймаут соединения.",
+  "llm_auth_error": "API ключ LLM отклонён. Проверьте credentials.",
+  "llm_unknown_status": "LLM статус неизвестен.",
+  "llm_auto_retry_countdown": "Auto-retry через {seconds}с…",
+  "llm_retry_now": "Retry now",
+  "llm_placeholder": "LLM недоступен...",
+  "llm_dismiss": "Скрыть"
 }

frontend/src/lib/models/AgentChat.StreamProcessor.svelte.ts

@@ -211,19 +211,20 @@ export class StreamProcessor {
       case "error":
         this.host.streamingState = "error";
         this.host.error = meta.detail ?? meta.code ?? "Unknown error";
-        // LLM provider error — update health status for banner
+        // LLM provider error — update health status for banner.
+        // Messages come from host._bannerMessageForStatus() or meta.detail from backend.
         switch (meta.code) {
           case "LLM_PROVIDER_UNAVAILABLE":
             this.host.llmStatus = "unavailable";
-            this.host.llmBannerMessage = meta.detail || "LLM провайдер недоступен";
+            this.host.llmBannerMessage = meta.detail || "";
             break;
           case "LLM_TIMEOUT":
             this.host.llmStatus = "timeout";
-            this.host.llmBannerMessage = meta.detail || "LLM провайдер не отвечает";
+            this.host.llmBannerMessage = meta.detail || "";
             break;
           case "LLM_AUTH_ERROR":
             this.host.llmStatus = "auth_error";
-            this.host.llmBannerMessage = meta.detail || "API ключ LLM отклонён";
+            this.host.llmBannerMessage = meta.detail || "";
             break;
         }
         break;

frontend/src/lib/models/AgentChatModel.svelte.ts

@@ -38,6 +38,7 @@ import {
 } from "$lib/api/assistant.js";
 import { addToast } from "$lib/toasts.svelte.js";
 import { log } from "$lib/cot-logger";
+import { t } from "$lib/i18n/index.svelte.js";
 import { type ConnectionManagerCallbacks, ConnectionManager } from "./AgentChat.ConnectionManager.svelte.js";
 import { type StreamProcessorHost, StreamProcessor } from "./AgentChat.StreamProcessor.svelte.js";
 import { LocalStorageManager } from "./AgentChat.LocalStorage.js";
@@ -711,10 +712,10 @@ export class AgentChatModel {
 
   private _bannerMessageForStatus(status: string): string {
     switch (status) {
-      case "unavailable": return "LLM провайдер недоступен. Проверьте подключение к upstream API.";
-      case "timeout":     return "LLM провайдер не отвечает. Таймаут соединения.";
-      case "auth_error":  return "API ключ LLM отклонён. Проверьте credentials.";
-      default:            return "LLM статус неизвестен.";
+      case "unavailable": return t.assistant?.llm_unavailable || "LLM провайдер недоступен. Проверьте подключение к upstream API.";
+      case "timeout":     return t.assistant?.llm_timeout || "LLM провайдер не отвечает. Таймаут соединения.";
+      case "auth_error":  return t.assistant?.llm_auth_error || "API ключ LLM отклонён. Проверьте credentials.";
+      default:            return t.assistant?.llm_unknown_status || "LLM статус неизвестен.";
     }
   }