feat: package skeleton — DESCRIPTION, NAMESPACE, session/manifest/cache/views

Minimal skeleton for uscogdata v0.1. Internal session layer with lazy
cog_open(), manifest fetch+validate+cache, view registration placeholder.
Depends on DuckDB >=1.0, httr2, jsonlite. inst/schemas/provenance-v1.json
ships the structured provenance JSON Schema.

R/config.R

@@ -0,0 +1,29 @@
+# R/config.R
+
+#' Package-private mutable state
+#' @noRd
+.uscogdata_env <- new.env(parent = emptyenv())
+
+.uscogdata_defaults <- list(
+  url               = "https://cloud.civilytics.org/s/REPLACE_WITH_SHARE_TOKEN/download/",
+  cache_dir         = NULL,
+  manifest_ttl_secs = 3600L
+)
+
+#' Resolve a config value: env var > option > default
+#' @noRd
+.cfg <- function(key) {
+  env_var <- paste0("USCOGDATA_", toupper(key))
+  v <- Sys.getenv(env_var, unset = NA)
+  if (!is.na(v) && nzchar(v)) return(v)
+  opt <- getOption(paste0("uscogdata.", key), default = NULL)
+  if (!is.null(opt)) return(opt)
+  .uscogdata_defaults[[key]]
+}
+
+.resolve_url <- function() .cfg("url")
+
+.resolve_cache_dir <- function() {
+  v <- .cfg("cache_dir")
+  if (is.null(v)) tools::R_user_dir("uscogdata", "cache") else v
+}