feat(gui): useProjection — the fifth framework hook seat through the standard kit

React half of the session-projection client base: the renderer contract gains
an open-key projections face on SessionMaybeProvideInfo (cellOf(key), distinct
from the static hooks roster), web-react mints projectionHook (per-bundle cache;
per-cell uSES binding via the shared observableHook cache; unresolved keys read
undefined through the absent source so hook order stays constant), standardKit
delivers kit.useProjection, and the runtime merges UseProjection into
SessionStandardProps/SessionMaybeStandardProps (overloads mirror useSession).
3 jsdom specs (kit delivery + live re-render, selector over undefined, faceless
bundle = all absent); existing direct-prop-feed specs gain the one-line stub the
new required seat mandates.

packages/client/ui-question/tests/question-composer.spec.tsx

@@ -25,6 +25,7 @@ const kit = {
   useSession: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<ConversationSnapshot>,
   useSessions: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<SessionListState>,
   useWorkspaces: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<WorkspaceListState>,
+  useProjection: (() => undefined) as never,
   useInput: (() => { throw new Error('unused') }) as never,
   inputActions: { setDraft: () => { throw new Error('unused') }, submit: () => { throw new Error('unused') } } as never,
 }