bookable_resources 1.0.0-alpha2

Second alpha. Still not for production sites: the data model and the forms may change before beta.

## Bookings of several days

- A booking that spans several days is listed once, with all its days, instead of once per day.
- Its days show as tiles in the summary and in a real tooltip on the calendar, and the days label counts every day.

## Notifications and reminders

- Every email is sent in its recipient's language.
- A series that moves together sends one email, not one per occurrence. Its date names the first occurrence, how many more there are and until when.
- A value that comes out empty in the body says "Not provided", in an element a theme can style.
- New tokens: the moment in pieces (weekday, day and time), a relative moment ("In 2 hours", "Tomorrow"), a long date where PHP has intl, and the My reservations URL.
- Reminders have their own tab under Configuration, at /admin/bookable-resources/reminders. Their body is composed like a notification's, and their button goes to My reservations.
- Notification settings and the log are buttons on the notifications list.

## Forms and pages

- Messages go to the theme's messages area by default, through core's MessageCommand. The corner stack is now a setting.
- Delete sits in the actions bar, on the side away from Save, and asks before deleting. Cancelling a reservation is a secondary button.
- The edit page sends you somewhere once a booking is saved or deleted.
- Every entity's edit page has the standard tabs.
- The group comes before the resource in the lists' filters and in My reservations.
- Deleting a group, a resource or an account also deletes what depends on it.

## Help

- A search over the help topics, in the reader's language, with accents and case ignored. No index, no cron, no search module.
- Headings say what each section is about, and a heading's own anchor is kept so translations keep it too.
- Topics for maintenance blocks, site builders and developers.
- CONTRIBUTING.md and AGENTS.md with the rules for every contributor, people and AI assistants alike.