Fix estimation: replace 20% infill with 50% material factor, 32 g/h speed

The 20% infill assumption ignored walls and solid layers which dominate
most prints. Validated against Bambu Lab Studio for a GF lid:
  model volume 26.09 cm³ × 0.50 × 1.24 g/cm³ = 16.2 g  (actual: 16.24 g)
  16.2 g / 32 g/h × 60 = 30 min                          (actual: 30.5 min)

New env vars (read at request time, no rebuild needed):
  MATERIAL_FACTOR=0.50        fraction of model volume that becomes filament
  PRINT_SPEED_G_PER_HOUR=32   matches Bambu Lab at normal quality

Card header now shows active assumptions including speed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/templates/job_detail.html

@@ -140,7 +140,10 @@
   <div class="card-header text-secondary small text-uppercase fw-normal" style="border-color:#21262d">
     Estimate
     <span class="text-secondary fw-normal ms-2" style="font-size:.7rem">
-      20 % infill · {{ estimation.price_per_kg }} €/kg · {{ estimation.vat_rate }}% VAT
+      {{ (estimation.material_factor * 100) | round | int }}% material factor
+      · {{ estimation.print_speed | int }} g/h
+      · {{ estimation.price_per_kg }} €/kg
+      · {{ estimation.vat_rate }}% VAT
     </span>
   </div>
   <div class="card-body">