Align cable sizing with DIN VDE 0298-4

AGENTS.md

@@ -607,10 +607,13 @@ circuit list (see `docs/cable-sizing-module.md`). Rules:
   by clicking a grid cell; cable cells keep the normal spreadsheet behavior.
 - It has no database table and no migration; `/api/cable-sizing/*` is
   stateless.
-- Reference data is IEC 60364-5-52:2009 Annex B. Change table values only with
-  a documented source in `docs/cable-sizing-module.md`; where sources differ,
-  use the lower value. Inputs outside the tables return no result instead of
-  assuming a factor of 1.
+- Current-carrying capacities and correction factors use
+  DIN VDE 0298-4:2023-06 with Berichtigung 1:2023-10; the exact scope and the
+  separate basis of voltage-drop and protection checks are documented in
+  `docs/cable-sizing-module.md`. Inputs outside the supported tables return no
+  result instead of assuming a factor of 1. Direct burial, grouped method E,
+  aluminium below 25 mm² and neutral-current sizing above 33 % third harmonic
+  remain unsupported until their required inputs or normative basis exist.
 - Inputs are prefilled from the circuit (power, phase, voltage, weighted cos φ,
   length, protective device) and remain editable; manual cable entry without
   a calculation stays possible.