fix: drop tsx dev dependency, run tests with node's native type stripping

The tsx postinstall pulls its own esbuild binary, which fails inside the
Docker build ("Expected 0.28.2 but got 0.27.7") and broke the deploy.
Tests now run on node --experimental-strip-types, so the image installs
nothing extra.

tests/printlayout.test.ts

@@ -1,7 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { layout, capacity, cutMarks, effectiveGap, recommendedGap, dpiCheck, type SheetSpec } from '../src/lib/printlayout';
-import { parseSizeMm, mmToPx, mmToPt, paperById, photoById, labelMm } from '../src/lib/paper';
+import { layout, capacity, cutMarks, effectiveGap, recommendedGap, dpiCheck, type SheetSpec } from '../src/lib/printlayout.ts';
+import { parseSizeMm, mmToPx, mmToPt, paperById, photoById, labelMm } from '../src/lib/paper.ts';
 
 const A4: SheetSpec = { wMm: 210, hMm: 297, marginMm: 5, gapMm: 12, bleedMm: 0, center: true };