Fix package validation and build workflows

[quantifish]

What changed

• honour requested coordinate reference systems in marine-reserve, CRA-label, and clipping helpers
• validate selector, resolution, and simplification inputs with actionable errors
• preserve legitimate zero-valued raster cells
• make brms and rmapshaper optional, feature-scoped dependencies
• exclude Quarto caches, rendered HTML assets, and unused vignette data from source builds
• add regression coverage for projections, invalid inputs, raster zeros, and standard-grid outputs
• refresh stale data-source links and generated vignette figures
• install Quarto explicitly in both GitHub Actions workflows and update checkout to v4
• remove the generated vignettes/projections.html artefact and fix pkgdown accessibility metadata

Why

Several exported helpers silently ignored projection arguments or failed with accidental object not found errors. Generated Quarto artefacts also entered source packages, while optional V8/BRMS-related functionality made basic package installation unnecessarily fragile.

Validation

• devtools::test(): 39 passed, 0 failed, 0 warnings
• rendered all four Quarto vignettes individually
• full R CMD build with vignettes: passed
• full R CMD check from the source tarball: Status: OK
• pkgdown::build_site_github_pages(new_process = FALSE, install = FALSE): passed with no site problems