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

src/components/SettingsModal.tsx

@@ -178,6 +178,12 @@ export function SettingsModal() {
   const vacuumDatabase = useGalleryStore((state) => state.vacuumDatabase);
   const getOrphanedThumbnailsInfo = useGalleryStore((state) => state.getOrphanedThumbnailsInfo);
   const cleanupOrphanedThumbnails = useGalleryStore((state) => state.cleanupOrphanedThumbnails);
+  const appVersion = useGalleryStore((state) => state.appVersion);
+  const updateStatus = useGalleryStore((state) => state.updateStatus);
+  const updateVersion = useGalleryStore((state) => state.updateVersion);
+  const updateError = useGalleryStore((state) => state.updateError);
+  const checkForUpdates = useGalleryStore((state) => state.checkForUpdates);
+  const installUpdate = useGalleryStore((state) => state.installUpdate);
 
   useEffect(() => {
     if (!settingsOpen) return;
@@ -578,6 +584,47 @@ export function SettingsModal() {
               </div>
             ) : (
               <div className="mt-8 space-y-9">
+                <SettingsGroup title="Updates">
+                  <SettingsItem
+                    label={
+                      <span className="inline-flex items-center gap-2.5">
+                        <span>Phokus {appVersion ? `v${appVersion}` : "—"}</span>
+                        {updateStatus === "available" || updateStatus === "downloading" || updateStatus === "installing" ? (
+                          <StatusPill tone="busy">v{updateVersion} available</StatusPill>
+                        ) : updateStatus === "upToDate" ? (
+                          <StatusPill tone="ready">Up to date</StatusPill>
+                        ) : null}
+                      </span>
+                    }
+                    description={
+                      updateStatus === "error" ? (
+                        <span className="text-amber-300/90">Update check failed: {updateError}</span>
+                      ) : updateStatus === "downloading" || updateStatus === "installing" ? (
+                        "Downloading update — the app will restart when it finishes."
+                      ) : (
+                        "Updates are checked quietly at launch and installed only when you choose."
+                      )
+                    }
+                  >
+                    {updateStatus === "available" ? (
+                      <button
+                        className="rounded-md border border-emerald-400/35 bg-emerald-500/15 px-3 py-1.5 text-xs text-emerald-200 transition-colors hover:bg-emerald-500/25"
+                        onClick={() => void installUpdate()}
+                      >
+                        Install &amp; restart
+                      </button>
+                    ) : (
+                      <button
+                        className="rounded-md border border-white/10 bg-white/[0.055] px-3 py-1.5 text-xs text-gray-300 transition-colors hover:bg-white/10 hover:text-white disabled:cursor-not-allowed disabled:opacity-45"
+                        onClick={() => void checkForUpdates()}
+                        disabled={updateStatus === "checking" || updateStatus === "downloading" || updateStatus === "installing"}
+                      >
+                        {updateStatus === "checking" ? "Checking..." : "Check for updates"}
+                      </button>
+                    )}
+                  </SettingsItem>
+                </SettingsGroup>
+
                 <SettingsGroup title="Storage & notifications">
                   <SettingsItem
                     label="App data folder"