Add example Rscripts for real-world workflows (multicore, SLURM)

[natalie-23-gill]

Problem

The quickstart vignette uses plan("multisession") which won't work for real datasets due to memory copying. New users don't have a clear template for how to actually run clustOpt in production.

Proposal

Add ready-to-adapt Rscript templates in inst/scripts/:

• run_clustopt_multicore.R — local machine with plan("multicore")
• run_clustopt_slurm.R — HPC with future.batchtools

These should show the real-world pattern: load data → sketch → free original object → SCTransform → PCA → run clust_opt → save results.

Users can copy and adapt these rather than translating the vignette.