Improve homepage dataset summary and searchable preview

[ANAMASGARD]

Description

Improves the homepage so its summary reflects records represented in traitsview, rather than counting every row in the full species, sites, and citations tables.

This PR:

• replaces the generic Metric/Value table with five observation-backed summary cards;
• renames unclear metrics using human-friendly labels;
• adds a searchable and paginated observation preview;
• removes IDs, checked, result_type, notes, timestamps, and other internal fields from the preview;
• replaces the bioenergy-only example with general summaries of the most frequently observed traits and species;
• adds responsive styling for the new homepage cards;
• adds focused tests for the homepage calculations and ranking logic;
• adds DT to the suggested dependencies and Quarto publishing workflow.

The summary values are calculated directly from traitsview:

• Observations: total observation rows
• Measured variables: distinct non-blank traits
• Represented species: distinct non-missing species_id values
• Contributing sites: distinct non-missing site_id values
• Data sources: distinct non-missing citation_id values

No species, site, citation, PFT, or junction tables are joined when calculating these metrics.

Related Issue(s)

Addresses #26

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Data update (changes to datasets)
• Documentation update
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have run devtools::check() with no new errors or warnings
• I have updated NEWS.md if applicable
• I have updated documentation if applicable
• I have added/updated tests if applicable

Validation

• devtools::test()
  • 30 tests passed
• quarto render --execute
  • full site rendered successfully
• devtools::check(args = c("--no-manual", "--no-build-vignettes"))
  • completed without new errors or warnings
  • three pre-existing NOTES remain related to Quarto frozen assets and the license stub
• git diff --check
  • passed
• Manually verified:
  • all five summary values;
  • table search and filtering;
  • sorting and pagination;
  • desktop and narrow-width layouts;
  • absence of internal database fields;
  • top-trait and top-species summaries.

Screenshots

Observation-backed homepage summary

Searchable observation preview

The preview below is filtered using Panicum, showing that client-side search works across the observation table.

Dataset diversity summaries

Data Changes

No packaged datasets or files under data-raw/ were modified.

Additional Notes

Biome and PFT summaries are not included because the packaged observation data does not contain a direct biome classification and the species-to-PFT relationship is many-to-many.

A map or biome/PFT summary would require maintainer guidance on the authoritative classification and how species assigned to multiple PFTs should be counted. These can be handled as follow-up work if requested.