Final naming decision. Renames the public component + element across the
board: React/Angular CopilotDrawer -> CopilotThreadsDrawer, the Lit element
copilotkit-drawer -> copilotkit-threads-drawer (tag, CopilotKitThreadsDrawer
class, COPILOTKIT_THREADS_DRAWER_TAG, defineCopilotKitThreadsDrawer), the
@copilotkit/web-components/drawer subpath -> /threads-drawer (+ src dir),
the CopilotThreadsDrawerRow directive / copilotThreadsDrawerRow input, and
all prose/test references. Generic types (DrawerThread, DrawerFilter),
--cpk-drawer-* tokens, and ::part names are unchanged. Behavior unchanged.
Shadow-DOM Lit element that renders the threads drawer: self-contained styles
with build-time token sync from react-core's theme, slot projection for custom
rows, license/upsell gating, filtering, and a mobile modal. View-state lives on
the element; domain state stays with the host. Multi-format build (ESM/CJS
externalize lit as a peer dep; UMD inlines lit so the CDN <script> path is
self-contained).