Restore per-provider form preferences and remove Auto model fallback

- Add per-provider preference storage: model, mode, thinkingByModel
- resolveFormState reads stored prefs as fallback between initial
  values and provider defaults
- setProviderFromUser seeds model/mode/thinking from stored prefs
  when switching providers
- persistFormPreferences writes full per-provider state on agent create
- Remove workingDir and serverId from stored preferences (redundant
  with workspace tab context)
- Simplify settings.tsx by removing preference-based server resolution

packages/app/src/app/settings.tsx

@@ -1,55 +1,23 @@
 import { useEffect, useMemo } from "react";
-import { ActivityIndicator, View } from "react-native";
 import { useRouter } from "expo-router";
-import { useUnistyles } from "react-native-unistyles";
 import { DraftAgentScreen } from "@/screens/agent/draft-agent-screen";
 import { useHosts } from "@/runtime/host-runtime";
-import { useFormPreferences } from "@/hooks/use-form-preferences";
 import { buildHostSettingsRoute } from "@/utils/host-routes";
 
 export default function LegacySettingsRoute() {
   const router = useRouter();
-  const { theme } = useUnistyles();
   const daemons = useHosts();
-  const { preferences, isLoading: preferencesLoading } = useFormPreferences();
 
   const targetServerId = useMemo(() => {
-    if (daemons.length === 0) {
-      return null;
-    }
-    if (preferences.serverId) {
-      const match = daemons.find((daemon) => daemon.serverId === preferences.serverId);
-      if (match) {
-        return match.serverId;
-      }
-    }
     return daemons[0]?.serverId ?? null;
-  }, [daemons, preferences.serverId]);
+  }, [daemons]);
 
   useEffect(() => {
-    if (preferencesLoading) {
-      return;
-    }
     if (!targetServerId) {
       return;
     }
     router.replace(buildHostSettingsRoute(targetServerId) as any);
-  }, [preferencesLoading, router, targetServerId]);
-
-  if (preferencesLoading) {
-    return (
-      <View
-        style={{
-          flex: 1,
-          justifyContent: "center",
-          alignItems: "center",
-          backgroundColor: theme.colors.surface0,
-        }}
-      >
-        <ActivityIndicator size="small" color={theme.colors.foregroundMuted} />
-      </View>
-    );
-  }
+  }, [router, targetServerId]);
 
   if (!targetServerId) {
     return <DraftAgentScreen />;