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/state.js

@@ -55,6 +55,10 @@ const $btnSave        = document.getElementById("btn-save-report");
 const $btnRetryUpdate = document.getElementById("btn-retry-update-status");
 const $btnRetryRun    = document.getElementById("btn-retry-update");
 const $btnCloseModal  = document.getElementById("btn-close-modal");
+const $btnCheckAgain  = document.getElementById("btn-check-again");
+const $updateCloseBtn = document.getElementById("update-close-btn");
+const $updPill        = document.getElementById("upd-pill");
+const $updLastChecked = document.getElementById("upd-last-checked");
 
 const $rebootOverlay  = document.getElementById("reboot-overlay");
 const $rebootMainCard = document.getElementById("reboot-main-card");
@@ -80,6 +84,8 @@ const $rebuildLog      = document.getElementById("rebuild-log");
 const $rebuildReboot   = document.getElementById("rebuild-reboot-btn");
 const $rebuildSave     = document.getElementById("rebuild-save-report");
 const $rebuildClose    = document.getElementById("rebuild-close-btn");
+const $rebuildCloseHdr = document.getElementById("rebuild-close-hdr");
+const $rebuildPill     = document.getElementById("rebuild-pill");
 
 // Feature Manager — domain setup modal
 const $domainSetupModal = document.getElementById("domain-setup-modal");