[CRAN feedback] Eliminate unsafe file writing: use tempdir() for all examples, vignettes, and tests

[villegar]

Summary:

• CRAN prohibits by-default writing to the user's home filespace, the package directory, or the working directory (getwd()) in examples, vignettes, or tests.

Feedback references:

• CRAN CookBook: Home filespace writing

Initial code review findings:

• In R/report.R, the default for file outputs is already tempfile(), but please confirm/extend this pattern in all user-writable function parameters.
• All examples, vignettes, and test code that writes files should explicitly use tempdir() (never package root, never working directory unless set within a temp directory).
• The vignette file deploy-local-datashield-server-with-opal.Rmd appears not to write output, but all future/output code must use tempdir() as root for all paths.

Checklist:

• Audit all file writing paths in R/, examples, vignettes, and tests
• Replace/force all file writing to use tempdir() or tempfile()
• Never write files in package root, home directory, or getwd()
• Add test to confirm forbidden file paths are not used by default
• Document with code comments as needed