feat(updater): self-update via GitHub Releases with launch check and settings UI

Phase 3 of the 0.1.0 release prep:
- tauri-plugin-updater + tauri-plugin-process wired into the builder, with
  updater:default / process:allow-restart capabilities
- bundle.createUpdaterArtifacts: true; endpoint points at the GitHub
  releases latest.json, pubkey baked into tauri.conf.json
- store: update status state machine (check / download progress / install)
  with a quiet launch check (prod only) that stays silent on network errors
- UI: dismissible update toast with download progress, plus an Updates group
  in Settings > General showing current version and manual check/install

package.json

@@ -22,6 +22,8 @@
     "@tauri-apps/plugin-fs": "^2.5.0",
     "@tauri-apps/plugin-notification": "^2.3.3",
     "@tauri-apps/plugin-opener": "^2",
+    "@tauri-apps/plugin-process": "^2.3.1",
+    "@tauri-apps/plugin-updater": "^2.10.1",
     "d3-force": "^3.0.0",
     "framer-motion": "^12.38.0",
     "react": "^19.1.0",