Add built-in updater, bump to 1.2.0

- predatord checks the Gitea releases every 6 hours, downloads the
  newest pacman package, verifies its SHA-256 from the release notes
  and installs it with `pacman -U` in a separate systemd unit
- Update notice and install button on the System page, in the sidebar
  and in the panel widget; `predatorctl update [--check] [--yes]`
- Optional API token for private repositories
- packaging/release.py builds and publishes releases in the format
  the updater expects

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plasmoid/org.predatorcontrol.panel/contents/ui/main.qml

@@ -72,6 +72,7 @@ PlasmoidItem {
         ? profileLabel(st.profile) + " · CPU " + temp(st.sensors.cpu_temp) + " · GPU " + temp(st.sensors.gpu_temp)
           + "\nFans " + (st.sensors.cpu_fan || 0) + " / " + (st.sensors.gpu_fan || 0) + " RPM"
           + "\nBattery " + batteryText()
+          + (st.update && st.update.available ? "\nUpdate " + st.update.latest + " available" : "")
         : "Service predatord not running"
 
     P5Support.DataSource {
@@ -352,6 +353,27 @@ PlasmoidItem {
                 }
             }
 
+            Kirigami.InlineMessage {
+                Layout.fillWidth: true
+                visible: root.ok && root.st.update !== null && root.st.update !== undefined && root.st.update.available
+                type: Kirigami.MessageType.Positive
+                text: root.ok && root.st.update ? (root.st.update_status === "running"
+                      ? "Installing update " + root.st.update.latest + "…"
+                      : "Update " + root.st.update.latest + " available") : ""
+                actions: [
+                    Kirigami.Action {
+                        text: "Install"
+                        icon.name: "update-none"
+                        visible: root.ok && root.st.update && root.st.update.can_install && root.st.update_status !== "running"
+                        onTriggered: root.run("update --yes")
+                    },
+                    Kirigami.Action {
+                        text: "Details"
+                        onTriggered: root.openPage("system")
+                    }
+                ]
+            }
+
             PC3.Label {
                 Layout.fillWidth: true
                 visible: root.lastError !== ""