Registry deduplication: duplicate Docker Hub entries in image destination picker

Description

When running ecloud compute app deploy and selecting an image destination, Docker Hub registries appear multiple times if ~/.docker/config.json contains multiple URL variants for the same registry (e.g., docker.io, index.docker.io, https://index.docker.io/v1/).

Example output:

Detected authenticated registries:
  dockerhub: mattmurrs/dev-test:latest
  dockerhub: mattmurrs/dev-test:latest
  dockerhub: mattmurrs/dev-test:latest

? Select image destination:
❯ mattmurrs/dev-test:latest
  mattmurrs/dev-test:latest
  mattmurrs/dev-test:latest
  Enter custom image reference

Root Cause

In packages/cli/src/utils/prompts.ts, getAvailableRegistries() deduplicates GCR entries using a Map (keyed by username), but Docker Hub and GHCR entries are pushed directly to the array without deduplication. Each auths entry in the Docker config that resolves to Docker Hub produces a separate registry entry.

Expected Behavior

Only one entry per unique registry type + username combination should appear in the picker.

Suggested Fix

Apply the same Map-based deduplication used for GCR to Docker Hub and GHCR entries (e.g., key by registryType:username).

Start in packages/cli/src/utils/prompts.ts and read getAvailableRegistries(), comparing the existing GCR Map deduplication with the Docker Hub and GHCR paths. Use Docker config entries with equivalent registry URL variants to verify that the image destination picker shows one entry per registry type and username.