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.

_pkgdown.yml

@@ -0,0 +1,13 @@
+url: ~
+template:
+  bootstrap: 5
+
+reference:
+  - title: Session
+    contents:
+      - has_keyword("internal")
+
+articles:
+  - title: Getting started
+    navbar: ~
+    contents: []