Non-blocking slot controls + npu/image-gen toggles (cancel mid-load)

[thinmintdev]

What

Extends the fire-and-forget pattern from the save/swap rework (#781) to every slot control surface so clicks register instantly and a slow-loading slot can be cancelled mid-load instead of waiting for the model to finish loading.

Why

Lifecycle controls awaited the backend POST, which blocks for the whole model-load (seconds-to-minutes). That:

1. Froze the card while the request was in flight, and
2. Disabled the Stop button during the transitional phase — so a user who started a slow load (or hit the wrong slot) had no way to cancel until it completed.

Changes

• SlotsView / SlotCard — runMutation fires (mutate, not mutateAsync) and toasts immediately. Stop is no longer gated by busy/transitional, so it stays live throughout a load. Start/Restart keep their double-trigger guards.
• SlotListRow — restart is fire-and-forget.
• NpuFlmStack — run→fire; the master switch is flip-to-cancel (unloads when loaded or mid-load); the modality toggle awaits only the fast config write, then fires the cold restart. Drops the long-lived busy flag that froze the whole trio during an FLM reload.
• InferencePane SlotControls (shared with the NPU trio) — Stop always cancelable.
• ComfyUI pane — doSwitch/doPin close the confirm dialog + toast on commit rather than after the round-trip (the switchover is already a 202-async arbiter flip; the status poll drives the transitional UI).

Toasts switched to present-progressive ("Stopping X…", "Restarting X…", "Loading NPU stack…") since the action is now in-flight rather than complete.

Test

• New regression: Stop stays enabled on a transitional slot and cancel fires /unload without waiting.
• Full UI e2e: 237 passed / 6 skipped.

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