Add auto-updater (Phase 1 #4)

- tauri-plugin-updater + tauri-plugin-process registered (Rust + npm)
- Updater endpoint: github.com/hoornet/wrystr/releases/latest/download/latest.json
- Ed25519 signing keypair generated; public key in tauri.conf.json;
  private key added to TAURI_SIGNING_PRIVATE_KEY GitHub secret
- Release workflow passes TAURI_SIGNING_PRIVATE_KEY env var so
  tauri-action signs artifacts and generates latest.json manifest
- useUpdater hook: checks for updates 5 s after startup (silent on
  error); exposes available, version, install(), dismiss()
- UpdateBanner: dismissible top-of-app bar shown when an update is
  available — "Update & restart" downloads, installs, and relaunches

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -13,6 +13,30 @@ import { AboutView } from "./components/shared/AboutView";
 import { ZapHistoryView } from "./components/zap/ZapHistoryView";
 import { DMView } from "./components/dm/DMView";
 import { useUIStore } from "./stores/ui";
+import { useUpdater } from "./hooks/useUpdater";
+
+function UpdateBanner() {
+  const { available, version, installing, error, install, dismiss } = useUpdater();
+  if (!available) return null;
+  return (
+    <div className="flex items-center justify-between px-4 py-2 bg-accent/10 border-b border-accent/30 text-[12px] shrink-0">
+      <span className="text-text">
+        Wrystr {version} is available.{" "}
+        {error && <span className="text-danger ml-1">{error}</span>}
+      </span>
+      <div className="flex items-center gap-3">
+        <button
+          onClick={install}
+          disabled={installing}
+          className="text-accent hover:text-accent-hover transition-colors disabled:opacity-50"
+        >
+          {installing ? "Installing…" : "Update & restart"}
+        </button>
+        <button onClick={dismiss} className="text-text-dim hover:text-text transition-colors">×</button>
+      </div>
+    </div>
+  );
+}
 
 function App() {
   const currentView = useUIStore((s) => s.currentView);
@@ -25,7 +49,9 @@ function App() {
   }
 
   return (
-    <div className="flex h-screen w-screen bg-bg">
+    <div className="flex flex-col h-screen w-screen bg-bg">
+      <UpdateBanner />
+      <div className="flex flex-1 min-h-0">
       <Sidebar />
       <main className="flex-1 min-w-0">
         {currentView === "feed" && <Feed />}
@@ -40,6 +66,7 @@ function App() {
         {currentView === "zaps" && <ZapHistoryView />}
         {currentView === "dm" && <DMView />}
       </main>
+      </div>
     </div>
   );
 }

src/hooks/useUpdater.ts

@@ -0,0 +1,64 @@
+import { useEffect, useState } from "react";
+import { check } from "@tauri-apps/plugin-updater";
+import { relaunch } from "@tauri-apps/plugin-process";
+
+interface UpdateState {
+  available: boolean;
+  version: string | null;
+  body: string | null;
+  installing: boolean;
+  error: string | null;
+  install: () => Promise<void>;
+  dismiss: () => void;
+}
+
+export function useUpdater(): UpdateState {
+  const [available, setAvailable] = useState(false);
+  const [version, setVersion] = useState<string | null>(null);
+  const [body, setBody] = useState<string | null>(null);
+  const [installing, setInstalling] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const [dismissed, setDismissed] = useState(false);
+
+  useEffect(() => {
+    // Check for updates ~5 s after startup (non-blocking)
+    const t = setTimeout(async () => {
+      try {
+        const update = await check();
+        if (update?.available) {
+          setAvailable(true);
+          setVersion(update.version);
+          setBody(update.body ?? null);
+        }
+      } catch {
+        // Update check failure is silent — network may be unavailable
+      }
+    }, 5000);
+    return () => clearTimeout(t);
+  }, []);
+
+  const install = async () => {
+    setInstalling(true);
+    setError(null);
+    try {
+      const update = await check();
+      if (update?.available) {
+        await update.downloadAndInstall();
+        await relaunch();
+      }
+    } catch (err) {
+      setError(String(err));
+      setInstalling(false);
+    }
+  };
+
+  return {
+    available: available && !dismissed,
+    version,
+    body,
+    installing,
+    error,
+    install,
+    dismiss: () => setDismissed(true),
+  };
+}