refactor: consolidate loading/error states and extract instance actions hook

Frontend:
- Create reusable DataStates components (LoadingState, ErrorState, EmptyState)
- Refactor 12 pages to use shared state components instead of inline JSX
- Extract useInstanceActions hook to eliminate session action duplication
- Update dashboard and sessions pages to use shared hook

OpenSpec:
- Archive completed mobile-app-usability change (44/44 tasks)
- Archive completed add-config-profiles change (15/15 tasks)

Quality: TypeScript check passes, production build succeeds

apps/web/src/pages/settings.tsx

@@ -2,6 +2,7 @@ import { useEffect, useState } from "react";
 import { Link, Outlet, useLocation, useOutletContext } from "react-router-dom";
 
 import { getUserConfig, updateUserConfig, type UserConfig, type UserConfigUpdate } from "../api/settings";
+import { EmptyState, ErrorState, LoadingState } from "../components/data-states";
 import { Icon } from "../components/icon";
 import { useAsyncData } from "../hooks/use-async-data";
 
@@ -71,17 +72,13 @@ export const SettingsPage = () => {
   };
 
   if (status === "loading") {
-    return <section className="stack"><p className="muted">Loading settings...</p></section>;
+    return <section className="stack"><LoadingState message="Loading settings..." /></section>;
   }
 
   if (status === "error") {
     return (
       <section className="stack">
-        <p>Failed to load settings</p>
-        <button className="secondary-button" onClick={() => reload()} type="button">
-          <Icon name="refresh" size="sm" />
-          Retry
-        </button>
+        <ErrorState message="Failed to load settings" onRetry={reload} />
       </section>
     );
   }