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/api/middleware_jwt.go

@@ -29,6 +29,7 @@ func requireJWT(secret []byte) func(http.Handler) http.Handler {
 				TeamID: claims.TeamID,
 				UserID: claims.Subject,
 				Email:  claims.Email,
+				Name:   claims.Name,
 				Role:   claims.Role,
 			})
 			next.ServeHTTP(w, r.WithContext(ctx))