feat(llm): topology event and configurable-provider directory

ctx.llm gains 'llm/adapters-updated' — a payload-free registry notification
emitted at every topology commit point (adapter routes registering or
disposing, directory entries appearing or withdrawing) with contained
observers and INVARIANT rethrow — plus registerConfigurableProviders/
listConfigurableProviders, the directory of routes an adapter plugin can
activate through configuration. llm-deepseek declares deepseek-official
(whole llm-deepseek section as profile); llm-pi-ai declares the full
installed catalog under providers.<provider> even while dormant, so the
web settings surface can offer every provider before any route exists.
The invariant companion asserts the registry stays readable at each
notification.

packages/llm/llm-deepseek/tests/adapter.spec.ts

@@ -555,8 +555,15 @@ describe('plugin registration and config', () => {
       baseURL: server.url,
     })
     expect(ctx.llm.listProviders()).toEqual([{ id: 'deepseek-official', name: 'DeepSeek' }])
+    expect(ctx.llm.listConfigurableProviders()).toEqual([{
+      provider: 'deepseek-official',
+      displayName: 'DeepSeek',
+      settingsNs: 'llm-deepseek',
+      settingsPath: [],
+    }])
     await fiber.dispose()
     expect(ctx.llm.listProviders()).toEqual([])
+    expect(ctx.llm.listConfigurableProviders()).toEqual([])
   })
 
   it('registers retryPolicy from the provider config', async () => {