test: add tests for AppController

Covers /apps, /apps/nameAvailable, /rao, /apps/:name (single + batch),
/query/app (max-entries cap, marketplace shape, hidden-app gating), and
/app-icon (default fallback, data-URL decoding, MIME allowlist, CDN
redirect). Routes are collected via PuterRouter; AppDriver is injected
through the shared `driversContainers` registry, and stub stores return
prefab app rows.

Closes #2969

Author: Salazareo