Collapse the lesson-type filter behind a Show Only button

The filter took a row of the booking calendar before a student had asked for
it. The view toggle and a new "Show Only" button now share one control row,
and the lesson-type list is revealed between that row and the calendar.

The list stays open across re-renders once revealed, and collapsing it leaves
the filter applied — the button keeps its active styling and carries the
number of ticked types, so a collapsed filter is never invisible.

Closes #119

Co-Authored-By: Claude Opus 5 <[email protected]>

CHANGELOG.md

@@ -14,7 +14,7 @@ each change under the current top section as you work.
 ## [1.2.2]
 
 ### Added
-- The booking calendar now has a **lesson type** filter above it, so a student browsing open times can narrow them to the types they actually want. Because not every open time can be booked as every private-lesson type — some times are tied to a specific type, others only take types of a matching length — the filter shows just the times bookable as the ticked types, and re-anchors the week view on the earliest one so it never opens on an empty week. Picking one of those times narrows the **Lesson type** picker on the registration form to the same list, and when only one type is left it is chosen automatically with its questions loaded. Tick nothing (or use **Show all types**) to see every open time as before. The filter is hidden when the studio only offers one private-lesson type.
+- The booking calendar now has a **Show Only** button beside the List/Week toggle that opens a lesson-type filter, so a student browsing open times can narrow them to the types they actually want. Because not every open time can be booked as every private-lesson type — some times are tied to a specific type, others only take types of a matching length — the filter shows just the times bookable as the ticked types, and re-anchors the week view on the earliest one so it never opens on an empty week. Picking one of those times narrows the **Lesson type** picker on the registration form to the same list, and when only one type is left it is chosen automatically with its questions loaded. The type list starts collapsed and can be tucked away again without losing the filter; the button shows how many types are ticked. Tick nothing (or use **Show all types**) to see every open time as before. The filter is hidden when the studio only offers one private-lesson type.
 - The **Group Classes** block can now be pinned to a single class, under **Classes shown → Class** in the block sidebar (shortcode: `[us_group_classes offering="…"]`). Pick a class and the block shows only that one, so it can be embedded on a page that describes the class. In this mode the class's own description is left out to avoid repeating the page copy — the card shows the schedule, instructor, price, enrolment deadline and the enrol/withdraw controls. Leaving it on **All classes** keeps the full browsable catalog with descriptions.
 - The **Student Registration** block can now send students onward to a page of your choosing once they finish registering. Its **After email confirmation** panel is now **After registration**: the page you pick there is where the link shown to a newly registered student points — the "Sign in to your account" link after they confirm their email, and a "Continue to your account" link for an invited student, who is signed in immediately. A new **Redirect automatically** option takes them straight there instead of showing the link. Registration errors are never skipped — a failed sign-up and an expired confirmation link still show their message on the page, as does the "check your email to confirm your address" step. The redirect needs a page to be chosen; with none set, students see the link (or, for invited students, just the confirmation) as before.