Release 1.2.2 stable — consolidated v1.2.1.x cycle

Promote the v1.2.1.x beta cycle to stable: version markers bumped
from 1.2.1.4-beta to 1.2.2 across version.txt, AppImage/package.json,
flask_server.py (3 places) and the four UI labels in login,
proxmox-dashboard, storage-overview and release-notes-modal.

Replace AppImage/ProxMenux-1.2.1.4-beta.AppImage with
ProxMenux-1.2.2.AppImage and regenerate the .sha256 sidecar
(097e2344675d4b21f1dd18c531c956c299a6507fbc3d0c9695418063581ba2b0).
The new binary is verified on all 4 lab hosts (.50 / .55 / .89 /
1.10) — same sha, all services active, runtime version markers
report 1.2.2.

CHANGELOG["1.2.2"] in release-notes-modal.tsx consolidates every beta
in the 1.2.1.x line (12 added / 13 changed / 18 fixed), and
CURRENT_VERSION_FEATURES is rewritten with the four stable highlights:
Health Monitor Thresholds, granular dismiss control (per-event
duration + Active Suppressions panel), Apprise notification channel
parity, and LXC update detection.

AppImage/components/proxmox-dashboard.tsx

@@ -858,7 +858,7 @@ export function ProxmoxDashboard() {
         </Tabs>
 
         <footer className="mt-8 md:mt-12 pt-4 md:pt-6 border-t border-border text-center text-xs md:text-sm text-muted-foreground">
-          <p className="font-medium mb-2">ProxMenux Monitor v1.2.1.4-beta</p>
+          <p className="font-medium mb-2">ProxMenux Monitor v1.2.2</p>
           <p>
             <a
               href="https://ko-fi.com/macrimi"