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/SettingsPanel.tsx

@@ -1,6 +1,8 @@
 import { useState, useEffect } from "react";
 import DockerSettings from "./DockerSettings";
 import AwsSettings from "./AwsSettings";
+import OllamaSettings from "./OllamaSettings";
+import OpenAiCompatibleSettings from "./OpenAiCompatibleSettings";
 import { useSettings } from "../../hooks/useSettings";
 import { useUpdates } from "../../hooks/useUpdates";
 import ClaudeInstructionsModal from "../projects/ClaudeInstructionsModal";
@@ -148,6 +150,10 @@ export default function SettingsPanel() {
 
       <AccordionSection id="backends" title="Backends" defaultOpen={false}>
         <AwsSettings />
+        <div className="pt-3 border-t border-[var(--border-color)]" />
+        <OllamaSettings />
+        <div className="pt-3 border-t border-[var(--border-color)]" />
+        <OpenAiCompatibleSettings />
       </AccordionSection>
 
       <AccordionSection id="container" title="Container" defaultOpen={false}>