v1.31.0

### Changes

- The batch save page gets a profile dropdown next to the "Save pages" button. The first entry keeps the current behaviour, the profile of each URL comes from the rules and from the profile selected in the options page, and the other entries apply one profile to every URL of the batch, rules included. The choice is remembered.
- Each URL of the batch shows the profile it will be saved with, and a URL that a rule maps to the disabled profile is flagged before saving.
- A URL skipped by the batch save because its rule maps it to the disabled profile stays in the list with a status saying so, instead of silently disappearing.

### Fixes

- Options page: the labels of the auto-configuration rules are aligned again, and the help text of "synchronize options" no longer pushes the button bar out of the dialog (#2020). The inserted help blocks broke the sibling selectors of the stylesheet.
- The first click on a context menu entry after the background woke up is no longer lost: the click handler now waits for the menus to be rebuilt before looking the entry up (#2008).
- The semi-transparent mask displayed while a page is being saved no longer darkens with the page's own `::backdrop` rule. The mask and the logs panel are top-layer popovers, and a page rule such as `::backdrop { background: rgba(51, 51, 51, .8) }` applied to their backdrop. Their `::before` and `::after` pseudo-elements are turned off as well, so a page rule cannot draw on them.
- The cancel button displayed while saving is aligned with the logs panel and uses the same colours in the light and dark schemes.
- Update single-file-core to 1.6.31: the link added next to a blocked video stays on the video instead of landing at the top of the page when the video sits directly in `<main>` or `<body>`, and the infobar host turns off the pseudo-elements a page stylesheet could draw on it.