Replace NODEJS_22_X with NODEJS_24_X across all nine Lambda NodejsFunction
definitions in lib/constructs/ (bedrock-agent, slack-handler, notion-sync,
po-sync, workorder-sync). Also add dependabot ignore for @types/node >=26
to prevent premature major bumps while we stay on the nodejs24.x runtime.
Both package.json files already carry @types/node ^24 — no pin change needed.
Refs #72
Per handbook Pinning Principle: exact pins are kept current by Dependabot version updates gated by CI + dependency review. Blanket ignores let pins rot (see today's fast-uri incident).
