Update Base Tag

Update the TAG ARG in the Dockerfile to the latest semver release of veecode/devportal-base.

Instructions

Fetch tags from Docker Hub (paginated)

Docker Hub returns at most 100 tags per page. Use WebFetch to query the first page, then check the next field in the response for additional pages:
```
URL: https://hub.docker.com/v2/repositories/veecode/devportal-base/tags/?page_size=100&ordering=last_updated
Prompt: List all semver tags (X.Y.Z format, no suffixes like -amd64 or -arm64). Also return the "next" URL if present.
```
If the response contains a next URL, fetch that page too and repeat until there are no more pages. Collect all tag names across all pages.