Rework Update System dialog to the approved design; match rebuild dialog

The update dialog kept the old bare title + spinner layout from the
previous theme. Rework it (and the rebuild dialog, for consistency) to
the approved The Hub dialog anatomy:

- Header: green chip icon, title, version chip, status pill
  (Checking… / Up to date / Updating… / Restart required / Update
  failed / Status unknown) and a header close button. A spinner appears
  in the header while an update is starting or running.
- System Details card: current version, release channel, and last
  checked (relative time, refreshed on every check).
- The log renders as a console with green "ok" and dim hint lines; the
  up-to-date result shows as a single green console line exactly once
  (the redundant status line is hidden in that state).
- Footer: Close plus a "Check again" primary action that re-runs the
  update check. Close and Check again are disabled while a check or
  update is in flight; all existing recovery actions (Save Error
  Report, Retry Status, Retry Update, Restart Entire System) keep their
  exact semantics.
- Opening the dialog now shows a "Checking…" state immediately while
  the existing reattach-then-check logic runs; reattaching to an
  in-progress update (page reload, RDP reconnect) is unchanged.

Sidebar Update System status tints now use the theme palette (red /
amber / blue / green), and the periodic background check refreshes the
dialog's "last checked" value.

Rebuild dialog gets the same header (icon, version chip, Applying… /
Done / Restart required / Failed pill, header close disabled while a
rebuild runs); its log stays hidden as before.

No API or state-machine changes: same endpoints, same polling, same
reattach and recovery behavior.

app/sovran_systemsos_web/static/js/events.js

@@ -4,6 +4,8 @@
 
 // if ($updateBtn) $updateBtn.addEventListener("click", openUpdateModal); // moved to sidebar in tiles.js
 if ($btnCloseModal) $btnCloseModal.addEventListener("click", closeUpdateModal);
+if ($btnCheckAgain) $btnCheckAgain.addEventListener("click", function() { openUpdateModal(); });
+if ($updateCloseBtn) $updateCloseBtn.addEventListener("click", closeUpdateModal);
 if ($btnReboot) $btnReboot.addEventListener("click", doReboot);
 if ($btnSave) $btnSave.addEventListener("click", saveErrorReport);
 if ($btnRetryUpdate) $btnRetryUpdate.addEventListener("click", retryUpdateStatus);
@@ -28,6 +30,7 @@ if ($logoutBtn) $logoutBtn.addEventListener("click", function () {
 
 // Rebuild modal
 if ($rebuildClose) $rebuildClose.addEventListener("click", closeRebuildModal);
+if ($rebuildCloseHdr) $rebuildCloseHdr.addEventListener("click", closeRebuildModal);
 if ($rebuildReboot) $rebuildReboot.addEventListener("click", doReboot);
 if ($rebuildSave) $rebuildSave.addEventListener("click", saveRebuildErrorReport);
 if ($rebuildModal) $rebuildModal.addEventListener("click", function(e) { if (e.target === $rebuildModal) closeRebuildModal(); });