Demo follow-ups: editable policy name, one-page signup, group classes in upcoming lessons, deletion cleanup

Five items from the latest demo pass:

- A policy's title can be edited from the Policies screen. Only the title
  moves; the slug is what the gates resolve policies by, so a rename can
  never detach a policy from acceptances already recorded against it.
- Signup is one page again. The studio's registration questions move from
  a second step behind "Next" onto the main form, in an "About you" panel
  above the students being added, and that panel also asks an adult
  student for their birth year (the same us_birth_year meta a child's
  uses). register.js disables and hides the whole panel for a pure
  guardian, since the questions describe a student.
- The password is re-scored on submit, not only as it is typed. zxcvbn's
  dictionary arrives after page load, so a password typed straight away
  was never scored at all and the first the student heard of it was the
  server rejecting the whole form.
- Group-class sessions appear alongside lessons wherever upcoming lessons
  are listed: the [us_scheduler] panel (students and instructors) and the
  admin student detail page. GroupClass\SessionSchedule derives them from
  Offering::sessionWindows(), the same derivation the billing scan uses.
  They carry kind = 'group_class' and no Cancel action - a session is one
  date in a term, not a booked slot.
- Deleting a user releases what the account was holding: each upcoming
  lesson is cancelled, its slot freed for rebooking, its pending payment
  voided, and active class enrolments cancelled. Past lessons and paid
  history are left alone.

Tests: composer test (851), composer lint, composer cs all pass.

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

CHANGELOG.md

@@ -13,6 +13,19 @@ each change under the current top section as you work.
 
 ## [1.4.1]
 
+### Added
+- **Group classes now appear in "Your upcoming lessons".** A class is stored as a term rather than as bookable slots, so nothing that listed lessons could ever show one — a student whose whole term was a group class saw an empty schedule, and an instructor teaching one saw nothing on their My Lessons page. Each remaining session of a class you are enrolled in now sorts in among your lessons by date, labelled **group class**; instructors see every session of the classes they teach, one row per session however many students are in it. A session has no Cancel button, because there is no such thing as cancelling one date of a term — withdrawing from the class is still done from the class page. A class whose date, time or length has not been filled in yields no sessions and is left out rather than shown at a time nobody chose.
+- The same group-class sessions now appear in **Upcoming lessons** on a student's admin detail page, so one table answers "what are they booked into next week?". Only upcoming ones — the **Group-class enrolments** table below already holds the history.
+- **A policy can be renamed.** The title was fixed at creation, so a typo or a change of wording meant creating a second policy and re-collecting everyone's acceptance. Renaming changes only what students read above the policy text: the slug stays put, so every version already accepted stays attached.
+
+### Fixed
+- **Deleting a student now gives back what they had booked.** WordPress deletes a user without knowing anything about lessons, so their bookings were left behind: the times stayed marked as booked and nobody else could take them, the lessons stayed on the instructor's schedule under a name that no longer resolved, and a group class kept a seat filled by nobody. Deleting an account now cancels each of its upcoming lessons, frees the time for rebooking, cancels its active class enrolments, and voids any payment still pending on them. Past lessons are left exactly as they are — they happened, and the payment report has to keep adding up. A paid lesson is not credited back: a credit could only be spent on the account being deleted, so a refund owed to someone who has left stays the studio's decision to make.
+- **A weak password is now caught before the form is submitted, not after.** The strength meter scores the password as you type, but zxcvbn's dictionary arrives a moment after the page loads — so a password typed straight away was never scored at all, and the first you heard of it was the server rejecting the whole form. The password is now re-scored on submit, so the verdict is always the one your password actually earns.
+
+### Changed
+- **Signup is one page again.** The studio's registration questions used to be a second step behind a **Next** button; they are now asked on the main form, in an **About you** panel above the students you are adding. What the studio needs to know about you is part of registering, not a sequel to it — and there is now one submit rather than three.
+- **Signup asks an adult student for their birth year**, the same four-digit year already asked of every student being registered on someone else's behalf. It is asked only when you are a student yourself — choosing **on behalf of one or more students** leaves the whole **About you** panel out, since those questions describe a student and in that case you are not one.
+
 ## [1.4.0]
 
 ### Added