feat(client): typed locale standard seat in the slot framework

Registrations declare a dictionary namespace (locale: NS) and the renderer
synthesizes a typed t prop for the entry's component from the installed
LocaleFace; the seat binding is re-derived per locale revision, so a language
switch hands out fresh t references and memoized consumers re-render through
ordinary shallow comparison. LocaleNamespaceMap is the declare-merge table
(namespace -> dictionary key union); TranslateNS<'ns'> is the
namespace-addressed translate type (namespace keys plus the shared common
vocabulary), carried by the t seat and by the locale service's typed bind.

LocaleService implements the face (lookup ns -> common -> zh -> key,
revision-carrying snapshots with subscriber isolation) and installs it
through the boot-once slots.installLocale seam, mirroring the renderer
install. The typed register(ns, {zh, en}) overload checks each dictionary
against the namespace's key union and requires every shipped locale, so a
missing or extra key and an unbalanced translation are compile errors.
Dictionary registration bumps the face revision without emitting
locale/change — the event now means exactly 'the active locale switched',
so registration-heavy boot cannot storm event listeners.

packages/client/ui-theme/tests/apply.spec.ts

@@ -73,7 +73,8 @@ describe('ui-theme apply', () => {
     const { instance, face } = faceOf(b.slots)
     // The inject-time re-sync sealed the init window: the mirror is current.
     expect(instance.getSnapshot().preference).toBe('dark')
-    expect(face.t('appearance.dark')).toBe('深色')
+    // Copy rides the standard locale seat: the entry declares the namespace.
+    expect(b.slots.entries(SLOT).find(e => e.component === AppearanceRow)!.locale).toBe(SETTINGS_NS)
 
     face.setTheme('system')
     expect(theme.getTheme().preference).toBe('system')