Update data preparation pipeline for native sf and Leaflet optimization
The Shiny application has been migrated to the `sf` library. Currently, legacy sp objects are being converted to sf at runtime using `sf::st_as_sf()` during the `readRDS()` process in `global.R`.
To improve application startup performance and map responsiveness, the data preparation pipeline should be updated to save `sf` objects directly into the `.rds` files, removing the need for on-the-fly conversion.
**Required Tasks:**
The data preparation script should be updated to:
1. Convert all spatial objects to native `sf` format.
2. Project all spatial data to `WGS84 (EPSG:4326)`.
3. Save finalized objects directly as `.rds`.
**Final Cleanup:**
Once the new data files are deployed, the `sf::st_as_sf()` conversion wrappers will be removed from `global.R`. This will significantly reduce the computational overhead during the application initialization phase.
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