Rework invite flow with callout cards and modal flow

[hendriebeats]

Replaces the flat invite table on the studies page with callout cards and a multi-step modal flow (review → accept/reject → select or create document). Also pulls the owner's name into the invite query so it can be shown to invitees.

Reviewer notes

Invite flow — new modal steps

• reviewShareModal / confirmRejectModal / selectDocumentModal are three new HTMX endpoints that render successive steps inside a single <dialog> element; each step swaps the dialog's innerHTML rather than navigating.
• The reject flow goes through a confirmation step before actually deleting the share token, to avoid accidental rejections.
• selectDocumentModal filters to "ungrouped" documents (those not already in a group study) because linking a document to two studies simultaneously would be incoherent.

Owner name on invite cards

• GetMyShareData now includes ownerName (shown on the invite card: "Alice has invited you to join…"). The join is a leftJoin_' on groupStudyOwner → user; it's nullable because a study might theoretically have no owner row yet.
• The join can produce multiple rows when a study has multiple owners, so getSharesForUser now deduplicates by token after mapping. The query already filtered by share.email = user.email so the set is small.
• Invites are now sorted by created ascending so the oldest invite appears first.

p-select "modern" variant

• Added a variant="modern" style to the custom <p-select> element for use inside the accept-invite modal, where the default inline style doesn't fit. It positions the dropdown with position: fixed so it escapes any overflow: hidden ancestors in the modal.

Safety fixes (tidy pass)

• head gdoc.editors → for_ (listToMaybe gdoc.editors): head is partial and would crash if a doc had no editors; silently skipping is correct behavior here.
• StopListenToDoc was sending docId (the new doc) instead of currentDocId (the doc being left), which would have caused the server to stop the wrong subscription on doc switch.
• All clickable <img> close icons replaced with <button type="button"> wrappers; the "Remove" button in the invite form given type="button" to prevent accidental form submission.
• Six logInfoSH/logInfo debug calls removed from ownershipMemberDoc.
• CSS typo a&hover → &:hover on study row hover rule.

Closes #101

[hendriebeats]

@boxyoman I think you'll like this one. It's better than the last designs I showed you and solves the problem of people not knowing they can link a document or create a new one intuitively.