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/src/index.ts

@@ -209,6 +209,9 @@ export function apply(ctx: Context, config: Config): void {
   }
 
   const adapter = new DeepSeekAdapter({ options, resolveApiKey })
+  ctx.llm.registerConfigurableProviders([
+    { provider: 'deepseek-official', displayName: 'DeepSeek', settingsNs: NS, settingsPath: [] },
+  ])
   // Route effects bind to this apply fiber via the stable `ctx` reference,
   // even when a swap runs inside the scoped settings callback below.
   let disposeRoute = ctx.llm.registerAdapter(['deepseek-official'], adapter)