docs(builder-codes): base.dev links use HTTP instead of HTTPS

**Path:** `docs/specifications/builder-codes/for-app-developers.mdx`

## Description

Line 9 links to `base.dev` twice using `http://`:

> Once your app is registered on [base.dev](http://base.dev/), the Base App will auto-append your Builder Code [...] This powers your onchain analytics in [base.dev](http://base.dev/) and qualifies you for potential future rewards.

## Suggested fix

Update both links to `https://base.dev/`.

Open docs/specifications/builder-codes/for-app-developers.mdx and inspect line 9. Update both base.dev links from HTTP to HTTPS, then verify that the two links use https://base.dev/.

Written by the indexing model from the issue text.