[Feature Request] Add Node.js 26 base image (public.ecr.aws/lambda/nodejs:26)

Node.js 26 was [released](https://nodejs.org/en/blog/release/v26.0.0) on 2026-05-05 as the upcoming LTS version.

Please add a new official Lambda base image for Node.js 26:
- `public.ecr.aws/lambda/nodejs:26`
- `public.ecr.aws/lambda/nodejs:26.x` (minor version tags)

This image is a prerequisite for:
- The Lambda `nodejs26.x` managed runtime
- The Runtime Interface Client (RIC) nodejs26.x support
- Other AWS services (SAM, CodeBuild, etc.) that depend on Lambda base images

**Node.js 26 highlights relevant to Lambda:**
- V8 v14.6 (NODE_MODULE_VERSION 147)
- Stable TypeScript support
- Temporal API enabled by default

If you're also waiting for this, please 👍 this issue.