Make the docker_start_app throttle per-app instead of global

[ClaydeCode]

Problem

docker_start_app is decorated @throttle(5) (shard_core/service/app_tools.py; decorator in shard_core/util/misc.py). The throttle is global per function, not per app name, and silently returns None when throttled. Consequence: a request to app B within 5 seconds of app A starting does not start B — the user stares at the splash screen until the next request or the next control_apps tick (which only starts always_on apps).

Proposal

Key the throttle on the app name (e.g. accept a key function: @throttle(5, key=lambda app_name, *a: app_name)), so each app has its own 5-second window. Keep the silent-drop semantics within one app's window (that is the intended dedupe).

Test: starting two different apps back-to-back must invoke docker for both; starting the same app twice within 5s must invoke docker once.

🤖 Generated with Claude Code

[ClaydeCode]

Fixed in #176 (#176), review requested from @max-tet.

docker_start_app's @throttle(5) is now keyed on the app name via a new optional key function on the throttle decorator, so each app gets its own 5s dedupe window — key=None keeps the old global behaviour unchanged. Same-app silent-drop within one window is preserved.

Tests per the issue: two different apps back-to-back both invoke docker; the same app twice within 5s invokes docker once (both mutation-verified to fail on the old global throttle). All required CI checks green.

AI-drafted, human-reviewed.