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-trajectory/tests/views.spec.tsx

@@ -77,6 +77,7 @@ function standaloneProps(nodes: ConversationSnapshot['nodes']): ConvViewProps {
     useSession: fakeSession(nodes).useSession,
     useSessions: emptySessions(),
     useWorkspaces: emptyWorkspaces(),
+    useProjection: (() => undefined) as never,
   } as unknown as ConvViewProps
 }
 
@@ -135,6 +136,7 @@ function mount(slots: SlotsService, nodes: ConversationSnapshot['nodes'] = NODES
       useSession={useSession}
       useSessions={emptySessions()}
       useWorkspaces={emptyWorkspaces()}
+      useProjection={(() => undefined) as never}
       useStore={bindSnapshotSelector(chat)}
       actions={chat.actions}
       renderSlot={renderSlot}
@@ -330,6 +332,7 @@ describe('deriveSubSpans (waterfall lanes)', () => {
       useSession: bindSnapshotSelector(store) as unknown as UseSession<ConversationSnapshot>,
       useSessions: emptySessions(),
       useWorkspaces: emptyWorkspaces(),
+      useProjection: (() => undefined) as never,
     } as unknown as ConvViewProps
     const view = render(createElement(WaterfallView as FC<ConvViewProps>, props))
     const lane = view.container.querySelector('[data-subspan]')
@@ -356,6 +359,7 @@ describe('deriveSubSpans (waterfall lanes)', () => {
       useSession: bindSnapshotSelector(store) as unknown as UseSession<ConversationSnapshot>,
       useSessions: emptySessions(),
       useWorkspaces: emptyWorkspaces(),
+      useProjection: (() => undefined) as never,
     } as unknown as ConvViewProps
     const view = render(createElement(WaterfallView as FC<ConvViewProps>, props))
     const bar = view.container.querySelector('[data-timing="unknown"]')