fix: scan on demand cooldowns

[TurtIeSocks]

• externalizes the cooldown into a hook so it works even when scanNext/scanZone isn't open
• persists the cooldown state between refreshes, but only in localStorage. Technically this can be worked around if someone cleared local storage but that's incredibly tedious and I think unlikely that any user will be abusing it that way. Maybe long term we could add it server side but for now I'm not that worried about it.