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.

.Rbuildignore

@@ -0,0 +1,11 @@
+^.*\.Rproj$
+^\.Rproj\.user$
+^_pkgdown\.yml$
+^docs$
+^pkgdown$
+^\.github$
+^LICENSE\.md$
+^\.git$
+^\.gitignore$
+\.gitkeep$
+^vignettes$