Typecheck tests against current types

tsx runs tests without type checking and tsconfig.json covers only src,
so 71 type errors had accumulated unnoticed. tsconfig.tests.json now
checks every test and helper, and npm run typecheck includes it.

Fixtures gain the fields the DTOs have grown since they were written
(manualQuantity, circuit apparent power/cos phi, downstream board loads,
section totals, building, cover and board info fields). Repository
lookups that return "row ?? null" now declare the null in their type,
which their callers already handle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/circuit-structure-projection.test.ts

@@ -42,7 +42,10 @@ function circuit(
     sortOrder: 10,
     isReserve: true,
     circuitTotalPower: 0,
+    circuitApparentPower: 0,
+    circuitCosPhi: 1,
     deviceRows: [],
+    downstreamBoardLoads: [],
   };
 }
 
@@ -124,6 +127,7 @@ describe("circuit structure projection", () => {
         name: "Leuchte",
         displayName: "Leuchte",
         quantity: 1,
+        manualQuantity: 1,
         powerPerUnit: 0.1,
         simultaneityFactor: 1,
         rowTotalPower: 0.1,