fix(cdk): enable isolatedModules for 18% faster Jest execution

ts-jest transpiles each file independently when isolatedModules is true,
skipping the full type-graph build. Type checking still runs separately
via `mise //cdk:compile`.

Before: 279.68s Jest / 4:40 wall
After:  229.90s Jest / 3:50 wall (~18% reduction)

Closes #194

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: scottschreckengaust

cdk/tsconfig.dev.json

@@ -17,6 +17,7 @@
     "noImplicitThis": true,
     "noUnusedLocals": false,
     "noUnusedParameters": false,
+    "isolatedModules": true,
     "resolveJsonModule": true,
     "strict": true,
     "strictNullChecks": true,