Add non-intrusive auto-updater

Tauri updater + process plugins. Checks Gitea Releases endpoint a few
seconds after launch; on a newer signed version shows a dismissible
bottom-right banner with download progress and auto-relaunch. Public
signing key in tauri.conf.json; release flow documented in RELEASING.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -29,6 +29,7 @@
   "bundle": {
     "active": true,
     "targets": "all",
+    "createUpdaterArtifacts": true,
     "icon": [
       "icons/32x32.png",
       "icons/128x128.png",
@@ -36,5 +37,16 @@
       "icons/icon.icns",
       "icons/icon.ico"
     ]
+  },
+  "plugins": {
+    "updater": {
+      "endpoints": [
+        "https://gitea.exbytestudios.com/ExbytePublicServices/exbyte-depot-viewer-perforce/releases/download/updater/latest.json"
+      ],
+      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IEQwODU3MDRBRTI3QkRDNTAKUldSUTNIdmlTbkNGMENZNFZib1lVMWFmOEVacDE2WVVUaGZIVWRTaURrUEJmbUJNajByTmdERkMK",
+      "windows": {
+        "installMode": "passive"
+      }
+    }
   }
 }