webapp: imaging progress dashboard + serial column on reports list

Adds end-to-end progress tracking for PXE imaging sessions and surfaces
each Blancco report's BIOS serial in the report list.

webapp:
  * services/imaging_status.py - JSON-per-serial state store under
    IMAGING_DIR (default /var/log/pxe-imaging). Atomic write via
    tempfile + rename. log_tail capped at 50 lines. Merges partial
    updates so clients can post just the current_stage tick.
  * config.py - new IMAGING_DIR env-overridable path.
  * services/csrf.py - explicit exempt list for machine-to-machine
    endpoints; /imaging/status is the first entry. Air-gapped LAN;
    trust-by-network for client posts.
  * app.py - four new routes:
      GET  /imaging               dashboard (renders all sessions)
      POST /imaging/status        client status push (JSON body)
      GET  /imaging/<serial>.json raw session JSON for ad-hoc polling
      POST /imaging/delete/<s>    clear a session from the dashboard
    Also parses each Blancco XML in the /reports list to surface
    system.serial + system.model columns.
  * templates/imaging.html - Bootstrap dashboard with per-session
    cards (state badge, progress bar, stage idx/total, mac, elapsed,
    log tail). meta http-equiv refresh=5 for auto-tick.
  * templates/base.html - new "Imaging Progress" nav entry.
  * templates/reports.html - Serial + Model columns added.

playbook:
  * shopfloor-setup/Shopfloor/lib/Send-PxeStatus.ps1 - new helper.
    Dot-source this then call Send-PxeStatus -Stage X -StageIndex N
    -StageTotal M from any stage script. BIOS serial via CIM, MAC via
    Get-NetAdapter, pctype + machinenumber from C:\Enrollment.
    Failures are swallowed to a local log so a network blip doesn't
    block imaging.
  * shopfloor-setup/Run-ShopfloorSetup.ps1 - dot-sources helper +
    posts at three coarse milestones (start, PPKG enrollment,
    handoff to Monitor-IntuneProgress).
  * shopfloor-setup/gea-shopfloor-keyence/09-Setup-Keyence.ps1 -
    posts at session start + after Install-FromManifest with
    succeeded/failed status derived from $rc. Other 09-Setup-*.ps1
    scripts can follow the same pattern.

ID is BIOS serial (stable across WinPE -> Windows transition and
across reboots, unlike hostname which is random pre-PPKG). Operator
already knows the serial of the bay they imaged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

webapp/templates/reports.html

@@ -17,6 +17,8 @@
       <thead class="table-light">
         <tr>
           <th>Filename</th>
+          <th>Serial</th>
+          <th>Model</th>
           <th>Type</th>
           <th>Size</th>
           <th>Date</th>
@@ -27,6 +29,8 @@
         {% for r in reports %}
         <tr>
           <td><code>{{ r.filename }}</code></td>
+          <td>{% if r.serial %}<code>{{ r.serial }}</code>{% else %}<span class="text-muted small">-</span>{% endif %}</td>
+          <td class="small">{{ r.model or '-' }}</td>
           <td><span class="badge bg-info text-dark">{{ r.type }}</span></td>
           <td>
             {% if r.size > 1048576 %}