[bmc08gt]

Implements the iOS side of the spec in code-payments/flipcash-client-orchestrator#124 (private-groups.md surfaces 1-2, group-invites.md surface 1).

• New Chat: "Create a New Group" is the first row, above Find Someone by Username. Community Chat stays last.
• After Create: the chat is pushed over the form as a normal forward push, then about 600 ms later (a delay sized to the push, since NavigationStack has no push-finished callback) the form and New Chat are removed from beneath it without animation (AppRouter.pushForCollapse(_:) / collapseTopmostPath(toTop:)). Back from the chat goes to the Chats list. Private and community creation share the call.
• Invite People sheet, group subjects only (plain and invite link): no Recent Chats or send path; the line "Send this link to the people you want to join your group" under the pill replaces the joined/expires line and the footnote; tiles are Copy, Share, QR Code; the group presenters moved from fullScreenCover to .sheet so it fits its content, and goes to large while the QR card shows. Profile, message and currency shares are unchanged. Analytics events are unchanged.
• Tests: group sheet layout and order, other subjects keep Recent Chats, pushForCollapse/collapseTopmostPath. Dropped the sheetMeta test with the helper.