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>

predator_control/cli.py

@@ -61,6 +61,10 @@ def main(argv=None):
     sp = sub.add_parser("battery-limit", help="80 %% charge limit")
     sp.add_argument("value", choices=["on", "off"])
 
+    sp = sub.add_parser("update", help="check for and install updates")
+    sp.add_argument("--check", action="store_true", help="only check, do not install")
+    sp.add_argument("--yes", "-y", action="store_true", help="install without asking")
+
     sp = sub.add_parser("open", help="open the main window")
     sp.add_argument("page", nargs="?", default="home")
 
@@ -139,6 +143,21 @@ def main(argv=None):
             if a.sync:
                 args["sync_keyboard"] = a.sync == "on"
             c.call("set_lightbar", **args)
+        elif a.cmd == "update":
+            u = c.call("check_update")
+            if not u["available"]:
+                print("Predator Control %s is up to date." % u["current"])
+                return 0
+            print("Update available: %s -> %s\n%s" % (u["current"], u["latest"], u["url"]))
+            if a.check:
+                return 0
+            if not u["can_install"]:
+                print("Automatic install needs the pacman package. Update with: git pull && sudo ./install.sh")
+                return 1
+            if not a.yes and sys.stdin.isatty() and input("Install now? [Y/n] ").strip().lower() not in ("", "y", "yes"):
+                return 0
+            c.call("install_update")
+            print("Installing %s in the background (journalctl -fu predator-control-update)." % u["asset"])
         elif a.cmd == "battery-limit":
             c.call("set_battery_limit", enabled=_bool(a.value))
     except DaemonError as e: