Add user names, team-scoped sandbox guard, and login robustness fixes

- Add name column to users (migration + sqlc regen); propagate through JWT
  claims, auth context, all auth/OAuth handlers, service layer, and frontend
- Sidebar and team page show name instead of email; team page splits Name/Email
  into separate columns
- Block sandbox creation in UI and API when user has no active team context
- loginTeam helper falls back to first active team when no default is set,
  fixing login for invited users with no is_default membership
- Exclude soft-deleted teams from GetDefaultTeamForUser, GetBYOCTeams queries
- Guard host creation against soft-deleted teams in service/host.go
- SwitchTeam re-fetches name from DB instead of trusting stale JWT claim
- Reset teams store on login so stale data from a previous session never persists
- Update openapi.yaml: add name to SignupRequest and AuthResponse schemas

internal/db/models.go

@@ -112,6 +112,7 @@ type User struct {
 	CreatedAt    pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt    pgtype.Timestamptz `json:"updated_at"`
 	IsAdmin      bool               `json:"is_admin"`
+	Name         string             `json:"name"`
 }
 
 type UsersTeam struct {