Add cost/time estimate card to job detail page

app/estimation.py:
  - 20% infill → material volume → weight (density per material)
  - print time at 20 g/h (conservative FDM average)
  - filament cost at FILAMENT_PRICE_PER_KG EUR/kg (env, default 15)
  - +20% misprint buffer, +30% gross profit margin
  - net price (ex. VAT) and gross price (VAT_RATE %, env, default 19)

Card shows three columns: Material & Time / Production cost / Suggested price.
Only rendered when STL volume is available. Assumptions shown in card header.

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

app/estimation.py

@@ -0,0 +1,55 @@
+"""Job cost and time estimation from STL geometry."""
+import os
+
+# g/cm³ per material — used to convert volume → weight
+_DENSITY: dict[str, float] = {
+    "PLA":   1.24,
+    "PETG":  1.27,
+    "ABS":   1.04,
+    "ASA":   1.07,
+    "TPU":   1.20,
+    "Nylon": 1.14,
+    "PC":    1.20,
+}
+_DEFAULT_DENSITY = 1.24
+
+# Conservative average FDM print speed for weight-based time estimate
+_PRINT_SPEED_G_PER_HOUR = 20.0
+
+
+def estimate(volume_ccm: float, material: str | None) -> dict:
+    """
+    Returns a cost/time estimate dict for one job.
+
+    Assumptions:
+      - 20 % infill  →  material used = volume * 0.20
+      - filament density from _DENSITY (default 1.24 g/cm³)
+      - print speed: 20 g/h (conservative FDM average)
+      - filament cost: FILAMENT_PRICE_PER_KG EUR / kg  (env, default 15)
+      - misprint buffer: +20 %
+      - gross profit margin: +30 %
+      - VAT: VAT_RATE %  (env, default 19)
+    """
+    vat_rate      = float(os.environ.get("VAT_RATE", 19))
+    price_per_kg  = float(os.environ.get("FILAMENT_PRICE_PER_KG", 15))
+    density       = _DENSITY.get(material or "", _DEFAULT_DENSITY)
+
+    material_ccm  = volume_ccm * 0.20
+    weight_g      = material_ccm * density
+    print_minutes = round((weight_g / _PRINT_SPEED_G_PER_HOUR) * 60)
+
+    filament_cost = weight_g / 1000 * price_per_kg
+    after_misprint = filament_cost * 1.20
+    net_price     = after_misprint * 1.30
+    gross_price   = net_price * (1 + vat_rate / 100)
+
+    return {
+        "material_ccm":    round(material_ccm, 2),
+        "weight_g":        round(weight_g, 1),
+        "print_minutes":   print_minutes,
+        "filament_cost":   round(filament_cost, 2),
+        "net_price":       round(net_price, 2),
+        "gross_price":     round(gross_price, 2),
+        "vat_rate":        vat_rate,
+        "price_per_kg":    price_per_kg,
+    }