fix: chat works with any configured provider + surfaces errors

The chat defaulted to a Claude model, so a user who saved only a Gemini key got
a silent failure (backend derived Anthropic, found no key, errored — and the UI
showed nothing).

- Backend: resolveModel now falls back to whichever provider actually has a key
  (preferring the configured one), so a Gemini key just works regardless of the
  picked model. Clear 400 if no provider is configured at all.
- Frontend: the chat seeds its model/effort from the saved AI config, and now
  surfaces request failures as both a persistent alert banner and a toast —
  never silent.
- Settings: switching provider auto-selects that provider's default model.
- Refreshed the model catalog to current ids (Gemini 2.5 Pro/Flash + 2.0 Flash;
  dropped the retired gemini-1.5-pro); per-provider default model updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/components/chat/chat-panel.tsx

@@ -2,6 +2,7 @@
 
 import { useChat } from "@ai-sdk/react";
 import { DefaultChatTransport } from "ai";
+import { AlertTriangle } from "lucide-react";
 import { nanoid } from "nanoid";
 import { useSearchParams } from "next/navigation";
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
@@ -38,8 +39,10 @@ import {
   getModel,
 } from "@/lib/ai-models";
 import type { TemetroUIMessage } from "@/lib/ai-chat";
+import { getAiConfig } from "@/lib/ai-settings";
 import { API_BASE_URL } from "@/lib/api-client";
 import { getPatient } from "@/lib/patients";
+import { notify } from "@/lib/toast";
 
 // Trigger: `/patient 10293` or just `/10293` — a client-side fast-path that
 // pulls records instantly without the LLM (also works offline).
@@ -65,9 +68,36 @@ export function ChatPanel() {
     [],
   );
 
-  const { messages, setMessages, sendMessage, status, stop } =
+  const { messages, setMessages, sendMessage, status, stop, error } =
     useChat<TemetroUIMessage>({ transport });
 
+  // Seed the model + effort from the user's saved AI config so the chat uses the
+  // provider they actually configured (e.g. their Gemini default), not a stale
+  // hardcoded default.
+  useEffect(() => {
+    let cancelled = false;
+    getAiConfig()
+      .then((cfg) => {
+        if (cancelled) return;
+        setModel(cfg.mode === "local" ? "ollama" : cfg.defaultModel);
+        setEffort(cfg.defaultEffort);
+      })
+      .catch(() => {
+        // Keep defaults; the chat still works and the backend falls back to any
+        // configured provider.
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  // Pop a toast whenever a request errors, so failures are never silent.
+  useEffect(() => {
+    if (error) {
+      notify.error(t("chat.error.title"), error.message || t("chat.error.body"));
+    }
+  }, [error, t]);
+
   const isCloudModel = (getModel(model)?.provider ?? "ollama") !== "ollama";
 
   // Run the LLM agent for a message (after any consent gate).
@@ -158,6 +188,21 @@ export function ChatPanel() {
     />
   );
 
+  const errorAlert = error ? (
+    <div
+      className="flex w-full items-start gap-2 rounded-2xl border border-destructive/40 bg-destructive/8 px-4 py-3 text-sm text-destructive-foreground"
+      role="alert"
+    >
+      <AlertTriangle className="mt-0.5 size-4 shrink-0" />
+      <div className="space-y-0.5">
+        <p className="font-medium">{t("chat.error.title")}</p>
+        <p className="text-destructive-foreground/90">
+          {error.message || t("chat.error.body")}
+        </p>
+      </div>
+    </div>
+  ) : null;
+
   const consentDialog = (
     <Dialog onOpenChange={setConsentOpen} open={consentOpen}>
       <DialogPopup>
@@ -191,7 +236,10 @@ export function ChatPanel() {
           <h1 className="text-center text-3xl font-semibold tracking-tight text-balance sm:text-4xl">
             {t("chat.heading")}
           </h1>
-          {promptInput}
+          <div className="flex w-full flex-col gap-3">
+            {errorAlert}
+            {promptInput}
+          </div>
         </div>
         {consentDialog}
       </div>
@@ -240,7 +288,10 @@ export function ChatPanel() {
         </ConversationContent>
         <ConversationScrollButton />
       </Conversation>
-      <div className="mx-auto w-full max-w-3xl px-4 pb-4">{promptInput}</div>
+      <div className="mx-auto flex w-full max-w-3xl flex-col gap-3 px-4 pb-4">
+        {errorAlert}
+        {promptInput}
+      </div>
       {consentDialog}
     </div>
   );

frontend/components/settings/settings-ai.tsx

@@ -71,6 +71,19 @@ export function AIPanel() {
   const set = <K extends keyof AiConfig>(key: K, value: AiConfig[K]) =>
     setConfig((prev) => ({ ...prev, [key]: value }));
 
+  // Switching provider: if the current default model doesn't belong to the new
+  // provider, pick that provider's first model so they never end up mismatched.
+  const setProvider = (provider: ApiProvider) =>
+    setConfig((prev) => {
+      const models = AI_MODELS.filter((m) => m.provider === provider);
+      const stillValid = models.some((m) => m.id === prev.defaultModel);
+      return {
+        ...prev,
+        provider,
+        defaultModel: stillValid ? prev.defaultModel : (models[0]?.id ?? prev.defaultModel),
+      };
+    });
+
   // Models available for the currently selected cloud provider.
   const providerModels = useMemo(
     () => AI_MODELS.filter((m) => m.provider === config.provider),
@@ -169,9 +182,7 @@ export function AIPanel() {
               <div className="space-y-1.5">
                 <FieldLabel>{t("settings.ai.provider")}</FieldLabel>
                 <Select
-                  onValueChange={(value) =>
-                    set("provider", value as ApiProvider)
-                  }
+                  onValueChange={(value) => setProvider(value as ApiProvider)}
                   value={config.provider}
                 >
                   <SelectTrigger>