Room info panel is now user-resizable (fixing a layout clip at narrow
widths), and every user-selection spot (room membership, admin ownership
transfer) uses a new searchable UserPicker instead of raw text input or
prompt(). Member rows fold role + actions into a single inline dropdown
instead of a row of buttons, so the member list stays usable as rooms grow.
Room invites (the accept/decline flow) are replaced by adding a user to a
room directly -- an admin/owner picks someone and they're a member
immediately, with a "you've been added" notification email instead of an
invite email. Drops the now-unused room_invites table.
Users can set a display name (shown instead of username in the message
list, room member list, TopBar, and admin Users tab) and upload a real
avatar, replacing the generated color-initial avatars everywhere a user
appears. Avatars are square-cropped and downscaled to 512px, reusing
app/storage.py's upload primitives from image uploads with a new square
option.
Two deliberate divergences from message-image handling, documented in
backend/README.md: the previous avatar file is deleted on replace/remove
(safe since it's strictly one file per user), and avatar serving is not
room-gated and uses a short cache (identity-addressed and mutable, unlike
a message image's permanent content-addressed URL).
Frontend: new ProfileModal reachable from the TopBar account menu;
AuthContext gains updateUser() so a profile change reflects instantly
everywhere without a refetch.