Swaps cdk.json app runner from 'npx ts-node --prefer-ts-exts' to 'npx tsx',
replaces ts-node with tsx 4.23.0 (matching sh-mcp), and takes typescript ~7.0.2
(the bump held back earlier because ts-node 10.x is incompatible with the TS7
compiler API). cdk synth + tsc pass; npm audit 0 vulns.