feat: initial econ-skm-score v0.1.0 (econ.skm_score@0.1.0)

Standardkostenmodell (Methode des Nationalen Normenkontrollrats):

  eur_per_year = P × F × T × h

  P  population (Fallzahl)
  F  frequency per year (Frequenz)
  T  tariff in €/h (Tarif)
  h  time per case in hours (Zeitaufwand)

Each item preserves the formula string so an auditor can
reconstruct the calculation from the Hub audit log without
re-running the module.

Per-duty tier flags propagate via the Regel-der-niedrigsten-Stufe
(Studie §6.7): the aggregate tier_lowest is the worst tier among
the duties, so any T4 (qualitative signal) ingredient drags the
whole report down to T4. That is intentional — it prevents
methodologically weak inputs from masquerading as confidence.

Reuse-lens: SKM is EU- and OECD-anerkannt. The Niederländer (ATR),
UK (Regulatory Policy Committee) and EU REFIT all use this
methodology. This module is meaningful far beyond lawheatmap.

Pure in-WASM, zero filesystem, zero network.

Reserved for next versions:

  - 0.2: confidence intervals (P/F/T/h Streuung → output band)
  - 0.3: industry-tariff lookup (DESTATIS Bruttoverdienst-Reihen)

Signed-off-by: flemming-it <sf@flemming.it>

rust-toolchain.toml

@@ -0,0 +1,4 @@
+[toolchain]
+channel = "1.86"
+targets = ["wasm32-wasip2"]
+components = ["rustfmt", "clippy"]