feat(ui-slots): bind inject hooks compartments into use<Name> selector hooks

Registrant-private reactive facts previously reached components as raw
observables that each component subscribed by hand (InputBar notices/
lexicon via uSES, SettingsRoot via a version/subscribe/getter triple).
The inject face now carries a reserved hooks compartment of bare
sources; the renderer binds each into a use<Name> selector hook through
the same machinery as the provide channel, so components consume
useNotices/useLexicon/useSections and never see a subscription
primitive. InputBar and SettingsRoot are the first two consumers.

packages/client/ui-conversation/tests/input-matrix.spec.tsx

@@ -42,6 +42,8 @@ function mountBar(shell: SessionInputShell, over?: { running?: boolean; disabled
     useInput: bindSnapshotSelector(shell.state),
     inputActions: shell.actions,
     keyboard: shell,
+    useNotices: bindSnapshotSelector(shell.notices),
+    useLexicon: bindSnapshotSelector(shell.lexicon),
     renderSlot: (() => null) as InputBarProps['renderSlot'],
     stop: vi.fn(),
     variant: 'composer',