refactor(curves): canonical axis Nm³/(h·m² membrane) for all diffuser suppliers

Previously each curve file stored x in whatever convention the vendor
used (per-element Nm³/h for Jäger/GVA, per-element Sm³/h for PIK/PRK,
per-m² for Aerostrip). That meant the diffuser physics couldn't read
the data uniformly — selecting Aerostrip vs Jäger would feed wildly
different axes to the same interpolator.

All five curves now use the same canonical X: specific air flux in
Nm³/(h·m² membrane). Y stays SSOTR in g O₂/(Nm³·m); coverage % is the
parametric key.

Per-file conversions:
- jaeger-jetflex-td-65-2-g-epdm-1000: x divided by 0.18 m² perforated
  area (stated on the data sheet).
- gva-elastox-r: x divided by 0.18 m² placeholder mirroring Jäger
  TD-65 (no real GVA sheet exists — see _meta note).
- aerostrip-phoenix: native already in Nm³/(h·m²) — no x change. _meta
  area normalised to 1.0 m² per "element" so users set `elements` =
  total installed membrane area in m².
- pik300, prk300 (Sulzer ABS 300 mm disc): native was Sm³/h/disc on
  X and g O₂/(Sm³·m) on Y. Converted to canonical Nm³ basis (DIN-1343)
  by X × 0.9319 / 0.07, Y × 1.0732. Each disc = 0.07 m² membrane.

Supplier naming fixed: pikprk → sulzer, aquaconsult → aquaconsult-entec.
PIK = perforated EPDM, PRK = perforated PUR.

Config schema: new diffuser.membraneAreaPerElement field (nullable,
default null) so a node can override the curve's stored area. When
null, specificClass reads _meta.membraneArea_m2_per_element from the
resolved curve.

246/246 generalFunctions tests still pass.

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

datasets/assetData/diffuser.json

@@ -34,8 +34,8 @@
             ]
         },
         {
-            "id": "aquaconsult",
-            "name": "Aquaconsult / Entec",
+            "id": "aquaconsult-entec",
+            "name": "Aquaconsult Anlagenbau (Entec)",
             "types": [
                 {
                     "id": "diffuser-strip",
@@ -51,15 +51,15 @@
             ]
         },
         {
-            "id": "pikprk",
-            "name": "PIK / PRK (vendor TBD)",
+            "id": "sulzer",
+            "name": "Sulzer ABS",
             "types": [
                 {
                     "id": "diffuser-disc",
                     "name": "Disc",
                     "models": [
-                        { "id": "pik300", "name": "PIK300", "units": ["Sm3/h", "Nm3/h"] },
-                        { "id": "prk300", "name": "PRK300", "units": ["Sm3/h", "Nm3/h"] }
+                        { "id": "pik300", "name": "PIK300 — perforated EPDM", "units": ["Nm3/h"] },
+                        { "id": "prk300", "name": "PRK300 — perforated PUR",  "units": ["Nm3/h"] }
                     ]
                 }
             ]