Add proposed cable-sizing module

Isolated module (mirrors src/external-model/ dependency direction) that
adds an on-demand, DIN VDE 0298-4 referenced cable cross-section
calculator: a click-on-a-circuit input mask for laying method,
insulation, ambient temperature, grouping and voltage-drop limit that
suggests a cross-section for the circuit cableCrossSection/cableLength
fields. Applying a suggestion goes through the existing circuit.update
command (expectedRevision, undo/redo) unchanged - nothing here writes
to circuits directly or touches the revision/command system. See
docs/cable-sizing-module.md for the full rationale, API contract,
verification status and maintenance plan. Proposal, not yet reviewed
by the project owner - see the docs file.

423 existing + 11 new tests pass, build:api/build:web/typecheck:scripts
clean.

src/server/controllers/cable-sizing.controller.ts

@@ -0,0 +1,80 @@
+import { randomUUID } from "node:crypto";
+import type { Request, Response } from "express";
+import { cableSizingRequestSchema } from "../../cable-sizing/domain/cable-sizing-contracts.js";
+import {
+  calculateCableSizing,
+  buildCableSizingAlerts,
+  LAYING_METHODS,
+  LAYING_METHOD_LABELS,
+  LAYING_METHOD_VERIFIED,
+  INSULATION_MATERIALS,
+  INSULATION_MATERIAL_LABELS,
+} from "../../cable-sizing/domain/cable-sizing-calculation.js";
+import { cableSizingCalculationRepository } from "../composition/application-repositories.js";
+
+// Stateless calculation, not a project command: no expectedRevision, no
+// circuit mutation here. The caller applies the result via the existing
+// circuit.update command (POST /api/projects/:projectId/commands) if the
+// user confirms it. See docs/cable-sizing-module.md.
+export async function calculateCableSizingHandler(req: Request, res: Response) {
+  const parsed = cableSizingRequestSchema.safeParse(req.body);
+  if (!parsed.success) {
+    return res.status(400).json({ error: parsed.error.flatten() });
+  }
+
+  const { context, ...input } = parsed.data;
+  const result = calculateCableSizing(input);
+  const alerts = buildCableSizingAlerts(input, result);
+
+  const entry = await cableSizingCalculationRepository.create({
+    id: randomUUID(),
+    projectId: context?.projectId ?? null,
+    circuitId: context?.circuitId ?? null,
+    equipmentIdentifier: context?.equipmentIdentifier ?? null,
+    input,
+    result,
+    appliedToCircuit: 0,
+  });
+
+  return res.status(201).json({ calculationId: entry.id, result, alerts });
+}
+
+export async function listLayingMethodsHandler(_req: Request, res: Response) {
+  return res.json(
+    LAYING_METHODS.map((method) => ({
+      method,
+      label: LAYING_METHOD_LABELS[method],
+      dataVerified: LAYING_METHOD_VERIFIED[method],
+    }))
+  );
+}
+
+export async function listInsulationMaterialsHandler(_req: Request, res: Response) {
+  return res.json(
+    INSULATION_MATERIALS.map((insulation) => ({
+      insulation,
+      label: INSULATION_MATERIAL_LABELS[insulation],
+    }))
+  );
+}
+
+export async function markCalculationAppliedHandler(req: Request, res: Response) {
+  const { calculationId } = req.params;
+  if (typeof calculationId !== "string") {
+    return res.status(400).json({ error: "Invalid calculationId" });
+  }
+  const updated = await cableSizingCalculationRepository.markApplied(calculationId);
+  if (!updated) {
+    return res.status(404).json({ error: "Calculation not found" });
+  }
+  return res.json(updated);
+}
+
+export async function listCalculationsForCircuitHandler(req: Request, res: Response) {
+  const { circuitId } = req.params;
+  if (typeof circuitId !== "string") {
+    return res.status(400).json({ error: "Invalid circuitId" });
+  }
+  const rows = await cableSizingCalculationRepository.listByCircuit(circuitId);
+  return res.json(rows);
+}