Give the component what the app shell was providing

The component built and typechecked in the previous commit, but only because
nothing had rendered it. Everything Element Call needs that `src/main.tsx`
side-loads was missing from it.

Its stylesheet: only main.tsx imported index.css, so the library build emitted
CSS-module styles with every `--cpd-*` and `--font-size-*` unresolved. Split
into base.css, which both the app and the component import, and the rules that
are about owning a page, which only the app does. The split is a straight move
— comment-stripped and sorted, the old file and the two new ones differ by
exactly one line — and that line is the deliberate part: `.no-scroll-body`
becomes `body.no-scroll-body`. Element Call adds that class to whatever it
treats as its root, and since the root can now be a container, `position:
fixed` would have taken that container out of the host's layout. Pinning the
page is what it always meant.

Its translations: `initializeElementCall` called `i18n.init` with neither
resources nor a backend, so every key would have rendered as itself. English is
bundled in. The app fetches locale files from URLs its own build emits, which a
host serving the library from somewhere else could not resolve, so how a host
picks a language is left open.

And the types a host needs: `HostBridge` alone is not enough to implement
`HostBridge` — `HostRequest`, `DeviceMuteState`, `DeviceMuteRequest` and
`JoinCallData` all appear in its signatures, and `ConfigOptions` in
`initializeElementCall`'s.

component/ElementCall.module.css

@@ -22,3 +22,11 @@ using an iframe. */
   -moz-osx-font-smoothing: grayscale;
   -webkit-tap-highlight-color: transparent;
 }
+
+/* Compound's overlay container, which holds tooltips and popovers, has to fill
+the container for the elements inside it to be positioned against it. The
+standalone page does the same for the container under `#root`. */
+.root > [data-overlay-container] {
+  position: relative;
+  block-size: 100%;
+}