Wire @crema/llm-providers-ui: multi-provider picker + AI persistence

Replaces the single-base-URL LLM settings with the new providers lib
(OpenAI, Anthropic, DeepSeek, Qwen, LM Studio). Settings/LLM hosts the
catalog-aware card; the /ai route builds adapters via buildAdapter()
and resolves API keys from the arcadia vault per-call (direct mode).
Anthropic skips the /v1/models probe (no such endpoint) and uses
catalog defaults; failed probes for keyed providers fall back to the
catalog instead of dropping to mock.

AI conversation now persists across navigation and refresh via a new
crema.ai.live localStorage key (separate from the compact-snapshot
key). useChat hydrates from initialMessages on mount, saves on every
change, and "Clear conversation" wipes both state and storage.

Vite needs explicit resolve.alias for @crema/llm-ui and
@crema/llm-providers-ui — when a sibling lib imports another @crema/*,
tsconfigPaths can't resolve it (the importing file isn't in this
project's tsconfig scope).

Adds docs/LLM_PROXY_CONTRACT.md describing the
POST /api/v1/ai/llm/chat endpoint the backend needs for proxy mode
(keys never leave the server). Direct mode works against today's
arcadia; proxy mode unblocks once that endpoint ships.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vite.config.ts

@@ -65,6 +65,12 @@ const arcadiaClientSrc = fileURLToPath(
 const arcadiaAuthUiSrc = fileURLToPath(
   new URL("../lib-arcadia-auth-ui/src", import.meta.url),
 )
+const llmUiSrc = fileURLToPath(
+  new URL("../lib-llm-ui/src", import.meta.url),
+)
+const llmProvidersUiSrc = fileURLToPath(
+  new URL("../lib-llm-providers-ui/src", import.meta.url),
+)
 
 // Sibling lib packages (lib-content-ui, lib-content-editor-ui) import bare
 // deps like clsx and @tiptap/* but have no node_modules of their own. Pin
@@ -118,6 +124,8 @@ export default defineConfig({
       "@crema/search-ui": `${searchUiSrc}/index.tsx`,
       "@crema/arcadia-client": `${arcadiaClientSrc}/index.tsx`,
       "@crema/arcadia-auth-ui": `${arcadiaAuthUiSrc}/index.tsx`,
+      "@crema/llm-ui": `${llmUiSrc}/index.tsx`,
+      "@crema/llm-providers-ui": `${llmProvidersUiSrc}/index.tsx`,
       ...sharedDepAliases,
     },
     dedupe: dedupeDeps,