webapp: fix review findings (imaging types, NIC status, iPXE gates)

- imaging: coerce client payload and stored session fields to str/int,
  drop lists/dicts; tiles template guards pctype/current_stage; POST
  rejects non-object bodies and non-string serials.
- nic_status: normalise every check-file entry; load nic.conf as-is with
  a [nic] fallback; split interface= lists; keep the check's binding while
  fresh, resolve wildcard sockets from the dnsmasq pin (never True for an
  excluded NIC); mark vanished NICs down; include role bridges; stale or
  future-dated files downgrade to warnings and drop evidence.
- Overview renders the network pill in its own try and shows
  'Network: unknown' when status fails.
- ipxe_update: read every Authenticode signature (all WIN_CERTIFICATE
  entries plus nested SPC_NESTED_SIGNATURE) with openssl; shim swap and
  install need both Microsoft UEFI CA 2011 and 2023; install re-reads
  each file (snponly ipxe.efi only); staged.json schema version, older
  records shown stale and refused; uhci counts as native USB.
- backups describe their files; risky rollbacks need a confirm flag.
- mac_folders: guarded listdir, cached describe, configured TFTP root,
  warning for a shim without ipxe.efi.
- evidence pack: years 2000..2100, 400 days inclusive.
- a11y role=group on quick ranges; progress bar stays full during 'shim'.
- tests/test_review_fixes.py: 29 unittest cases incl. both real shims.

webapp/templates/reports.html

@@ -71,7 +71,7 @@
         <label class="sub" style="display: flex; flex-direction: column; gap: 4px">To
           <input id="evidenceTo" type="date" name="to" value="{{ pack_to }}" class="field" required></label>
       </div>
-      <div style="display: flex; gap: 6px; flex-wrap: wrap" aria-label="Quick ranges">
+      <div style="display: flex; gap: 6px; flex-wrap: wrap" role="group" aria-label="Quick ranges">
         <button type="button" class="fbtn" data-range="last-month">Last month</button>
         <button type="button" class="fbtn" data-range="last-3-months">Last 3 months</button>
         <button type="button" class="fbtn" data-range="this-month">This month</button>