Add global backend defaults with runtime fallback

New fields: GlobalAwsSettings.default_model_id, plus
GlobalOllamaSettings and GlobalOpenAiCompatibleSettings (base_url +
default_model_id each). When a per-project base_url or model_id is
blank, the container env vars and config fingerprints fall back to
the global value. Container recreation is triggered whenever the
resolved value changes, so editing a global default updates existing
projects on next start.

UI: added the new fields to AwsSettings and two new global settings
components, slotted into the Backends accordion.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/src/components/settings/OllamaSettings.tsx

@@ -0,0 +1,53 @@
+import { useSettings } from "../../hooks/useSettings";
+import Tooltip from "../ui/Tooltip";
+
+export default function OllamaSettings() {
+  const { appSettings, saveSettings } = useSettings();
+
+  const globalOllama = appSettings?.global_ollama ?? {
+    base_url: null,
+    default_model_id: null,
+  };
+
+  const handleChange = async (field: "base_url" | "default_model_id", value: string) => {
+    if (!appSettings) return;
+    await saveSettings({
+      ...appSettings,
+      global_ollama: { ...globalOllama, [field]: value || null },
+    });
+  };
+
+  return (
+    <div>
+      <label className="block text-sm font-medium mb-2">Ollama Configuration</label>
+      <div className="space-y-3 text-sm">
+        <p className="text-xs text-[var(--text-secondary)]">
+          Global Ollama defaults. Used when a per-project field is blank.
+          Changes here require a container rebuild to take effect.
+        </p>
+
+        <div>
+          <span className="text-[var(--text-secondary)] text-xs block mb-1">Default Base URL<Tooltip text="URL of your Ollama server. Used when a per-project Ollama base URL is blank." /></span>
+          <input
+            type="text"
+            value={globalOllama.base_url ?? ""}
+            onChange={(e) => handleChange("base_url", e.target.value)}
+            placeholder="http://host.docker.internal:11434"
+            className="w-full px-2 py-1.5 text-xs bg-[var(--bg-primary)] border border-[var(--border-color)] rounded focus:outline-none focus:border-[var(--accent)]"
+          />
+        </div>
+
+        <div>
+          <span className="text-[var(--text-secondary)] text-xs block mb-1">Default Model<Tooltip text="Default Ollama model name. Used when a per-project Ollama model is blank." /></span>
+          <input
+            type="text"
+            value={globalOllama.default_model_id ?? ""}
+            onChange={(e) => handleChange("default_model_id", e.target.value)}
+            placeholder="qwen3.5:27b"
+            className="w-full px-2 py-1.5 text-xs bg-[var(--bg-primary)] border border-[var(--border-color)] rounded focus:outline-none focus:border-[var(--accent)]"
+          />
+        </div>
+      </div>
+    </div>
+  );
+}