refactor: drop Desktop beta-settings check; gate hint on LogsTab flag

Docker Desktop is removing the "Enable Logs view" beta setting, so drop
the /app/settings check and rely on /features alone. With the setting
gate gone, the compose hook subprocess would print the Logs view hint
regardless of LogsTab; add a flag check in handleHook. Consolidate
engine-label discovery and feature-flag evaluation into internal/desktop.

Signed-off-by: Guillaume Lours <glours@users.noreply.github.com>