Add option to disable addon on current domain

[sirati]

When this addon breaks someone's workflow it would be extremely important to have the option to just disable it for a domain, so as to not having to wait till a fix is in.

[rbalogic]

I think this should be handled separately from #510

The Claude issue looks like a correctness bug in fragment parsing/serialization and should be fixed directly. This issue, though, is still valid as a broader resilience feature: when ClearURLs breaks a workflow on a specific site, users need a fast way to disable it there without turning the addon off globally.

My plan is to treat this as a separate feature PR:

• add a persisted per-site/domain disable list
• expose it in the popup as something like Disable on this site
• short-circuit request cleaning for disabled sites

That way the bugfix can ship independently, and this feature still provides an escape hatch for future site-specific breakage.