Change HandleWebSocket to use r.URL.Path as the room identifier instead
of r.URL.Query().Get("room"). This enables clean URL-based room routing
(e.g., ws://host/room-a) without query strings.
Update test helpers (dialTestHub, dialWSWithRoom) to connect via path
segments and fix direct broadcast channel tests to use path-style room
names (with leading slash).
All existing tests pass — clients connecting to / get the default room.
🤖 Assisted by the code-assist SOP
5bd08409dc