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-bar.spec.tsx

@@ -91,6 +91,8 @@ function bench(over?: BenchOptions) {
     useInput: bindSnapshotSelector(shell.state),
     inputActions: shell.actions,
     keyboard: shell,
+    useNotices: bindSnapshotSelector(shell.notices),
+    useLexicon: bindSnapshotSelector(shell.lexicon),
     stop,
     renderSlot,
     variant: over?.variant ?? 'composer',