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-conversation/tests/skeleton.spec.tsx

@@ -93,6 +93,7 @@ function mount(
           useSession={useSession}
           useSessions={props.useSessions}
           useWorkspaces={props.useWorkspaces}
+          useProjection={(() => undefined) as never}
           useInput={useInput}
           inputActions={inputActions}
           useStore={bindSnapshotSelector(chat)}
@@ -115,6 +116,7 @@ function mount(
           useSession={useSession}
           useSessions={props.useSessions}
           useWorkspaces={props.useWorkspaces}
+          useProjection={(() => undefined) as never}
           useInput={useInput}
           inputActions={inputActions}
           keyboard={wiring}
@@ -133,6 +135,7 @@ function mount(
     useSession,
     useSessions: bindSnapshotSelector(sessions),
     useWorkspaces: bindSnapshotSelector(workspaces),
+    useProjection: (() => undefined) as never,
     useInput,
     inputActions,
     renderSlot,