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>

package-lock.json

@@ -12,6 +12,8 @@
         "@tailwindcss/vite": "^4.2.1",
         "@tauri-apps/api": "^2",
         "@tauri-apps/plugin-opener": "^2",
+        "@tauri-apps/plugin-process": "^2.3.1",
+        "@tauri-apps/plugin-updater": "^2.10.0",
         "@types/dompurify": "^3.0.5",
         "dompurify": "^3.3.2",
         "marked": "^17.0.4",
@@ -1869,6 +1871,24 @@
         "@tauri-apps/api": "^2.8.0"
       }
     },
+    "node_modules/@tauri-apps/plugin-process": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-process/-/plugin-process-2.3.1.tgz",
+      "integrity": "sha512-nCa4fGVaDL/B9ai03VyPOjfAHRHSBz5v6F/ObsB73r/dA3MHHhZtldaDMIc0V/pnUw9ehzr2iEG+XkSEyC0JJA==",
+      "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.8.0"
+      }
+    },
+    "node_modules/@tauri-apps/plugin-updater": {
+      "version": "2.10.0",
+      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-updater/-/plugin-updater-2.10.0.tgz",
+      "integrity": "sha512-ljN8jPlnT0aSn8ecYhuBib84alxfMx6Hc8vJSKMJyzGbTPFZAC44T2I1QNFZssgWKrAlofvJqCC6Rr472JWfkQ==",
+      "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.10.1"
+      }
+    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",