gplay apps (registry + app details)

Two jobs: gplay's local registry of packages, and an app's App details record. Shared conventions (auth, --package, output, exit codes) live in gplay-cli-usage.

Local registry vs. server-side discovery

Two different questions, two commands:

• "What have I chosen to work on?" → apps list reads gplay's local registry: the packages you have apps add-ed under the active Account. The classic Android Publisher API has no apps.list endpoint, so this working set is gplay's own record, not a Play read.
• "What can this credential actually reach?" → apps accessible list is a server-authoritative inventory, straight from Google via the Play Developer Reporting apps.search method (least-privilege reporting scope, no local-registry fallback).