Add BYOC page, admin section, and is_byoc team visibility gating

- Frontend: BYOC hosts page (/dashboard/byoc) with register/delete flows,
  shimmer loading, pulsing online status, animated token reveal checkmark
- Frontend: Admin section (/admin/hosts) with platform + BYOC tabs, stat
  pills, skeleton loading, slide-in animations for new rows
- Frontend: AdminSidebar component with accent top bar and admin pill badge
- Frontend: BYOC nav item shown only when team.is_byoc is true (derived
  from teams store, not JWT); disabled for members
- Frontend: Admin shield button in Sidebar, visible only to platform admins
- Backend: is_admin in JWT claims + requireAdmin middleware (DB-validated)
- Backend: is_byoc added to teamResponse so frontend derives visibility
  from fresh team data rather than stale JWT fields
- Backend: SetBYOC admin endpoint (PUT /v1/admin/teams/{id}/byoc)
- Backend: Admin hosts list enriches BYOC entries with team_name
- Host agent: load .env file via godotenv on startup

internal/service/team.go

@@ -374,3 +374,27 @@ func (s *TeamService) LeaveTeam(ctx context.Context, teamID, callerUserID string
 func (s *TeamService) SearchUsersByEmailPrefix(ctx context.Context, prefix string) ([]db.SearchUsersByEmailPrefixRow, error) {
 	return s.DB.SearchUsersByEmailPrefix(ctx, pgtype.Text{String: prefix, Valid: true})
 }
+
+// SetBYOC enables the BYOC feature flag for a team. Once enabled, BYOC cannot
+// be disabled — it is a one-way transition.
+// Admin-only — the caller must verify admin status before invoking this.
+func (s *TeamService) SetBYOC(ctx context.Context, teamID string, enabled bool) error {
+	team, err := s.DB.GetTeam(ctx, teamID)
+	if err != nil {
+		return fmt.Errorf("team not found: %w", err)
+	}
+	if team.DeletedAt.Valid {
+		return fmt.Errorf("team not found")
+	}
+	if !enabled {
+		return fmt.Errorf("invalid request: BYOC cannot be disabled once enabled")
+	}
+	if team.IsByoc {
+		// Already enabled — idempotent, no-op.
+		return nil
+	}
+	if err := s.DB.SetTeamBYOC(ctx, db.SetTeamBYOCParams{ID: teamID, IsByoc: true}); err != nil {
+		return fmt.Errorf("set byoc: %w", err)
+	}
+	return nil
+}