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/curves/aerostrip-phoenix.json

@@ -4,6 +4,8 @@
         "type": "Strip",
         "model": "AEROSTRIP",
         "membrane": "PHOENIX",
+        "membraneArea_m2_per_element": 1.0,
+        "membraneArea_m2_per_element_note": "Aerostrip strips are sized continuously rather than as discrete fixed-area elements. Setting per-element area to 1.0 m² is a normalisation choice: configure the diffuser node with `elements` equal to the total installed strip membrane area in m².",
         "stdAir": { "temp_C": 0, "pressure_mbar": 1013.25, "RH_pct": 0 },
         "coverageBasis": "bottom-coverage-pct",
         "coverageReference": [5, 10, 15, 20],
@@ -12,10 +14,10 @@
         "yAxisBasis": "ssotr-g-per-Nm3-per-m",
         "waterDepth_m": 4.75,
         "sources": [
-            "Floris de Winter (Entec Holland) email to R. de Ren on 2023-11-22 — tabulated SOTE [%] at 4.75 m water depth for bottom coverage 5/10/15/20 % at fluxes 10/25/40/55/70 Nm3/(h*m2 membrane). Original chart in 'SSOTE_4.75m different density.pdf'.",
+            "Floris de Winter (Entec Holland) email to R. de Ren on 2023-11-22 — tabulated SOTE [%] at 4.75 m water depth for bottom coverage 5/10/15/20 % at fluxes 10/25/40/55/70 Nm³/(h*m² membrane). Original chart in 'SSOTE_4.75m different density.pdf'.",
             "'SSOTR_dP.pdf' — AEROSTRIP fine-bubble diffuser SSOTR + Druckverlust (DWP) chart at water depth 4.05 m, blow-in depth 4.00 m, 21 % bottom coverage. Used for the DWP curve only (read off the vector chart)."
         ],
-        "note": "X-axis is flux per m² of membrane area, NOT per element. The existing diffuser specificClass passes `flow_per_element` to the interpolator — if you wire an AEROSTRIP model in, you must either set elements/area such that flow_per_element == flux_per_m2_membrane, OR extend _calcOtrPressure to apply the membrane-area conversion. SSOTR values are SOTE [%] / water_depth_m * 0.299 kg-O2/Nm3 * 10 (linear depth scaling). DWP curve was measured at 21 % bottom coverage; pressure loss is intrinsic to the diffuser geometry so the curve is shared across coverage values."
+        "note": "SSOTR values are SOTE [%] / water_depth_m × 0.299 kg-O₂/Nm³ × 10 (linear depth scaling). DWP curve was measured at 21 % bottom coverage; pressure loss is intrinsic to the diffuser geometry so the curve is shared across coverage values (single 'p_curve' entry under key '0')."
     },
     "sote_curve": {
         "5":  { "x": [10, 25, 40, 55, 70], "y": [34.20, 28.75, 26.16, 24.89, 24.19] },
@@ -36,7 +38,7 @@
         "20": { "x": [10, 25, 40, 55, 70], "y": [27.57, 23.18, 21.10, 20.06, 19.49] }
     },
     "p_curve": {
-        "21": {
+        "0": {
             "x": [5, 10, 25, 40, 55, 70, 80],
             "y": [46.0, 47.3, 51.1, 54.9, 58.7, 62.4, 65.0]
         }