feat(agent): add llm assistant chat with api tools (task 88)

OpenAI-compatible client with mock fallback, tool-calling loop, and /assistant UI.

Tools map to /api/v1/ endpoints per ADR 0006 direct-tools decision.

src/lib/llm/config.ts

@@ -0,0 +1,30 @@
+export type LlmProviderKind = "mock" | "openai";
+
+export type LlmConfig = {
+  provider: LlmProviderKind;
+  baseUrl: string | null;
+  apiKey: string | null;
+  model: string;
+};
+
+export function getLlmConfig(): LlmConfig {
+  const providerEnv = process.env.LLM_PROVIDER?.trim().toLowerCase();
+  const baseUrl = process.env.LLM_BASE_URL?.trim() || null;
+  const apiKey = process.env.LLM_API_KEY?.trim() || null;
+  const model = process.env.LLM_MODEL?.trim() || "llama3.2";
+
+  if (providerEnv === "mock") {
+    return { provider: "mock", baseUrl: null, apiKey: null, model };
+  }
+
+  if (!baseUrl) {
+    return { provider: "mock", baseUrl: null, apiKey: null, model };
+  }
+
+  return { provider: "openai", baseUrl, apiKey, model };
+}
+
+export function isLlmConfigured(): boolean {
+  const config = getLlmConfig();
+  return config.provider === "openai" && Boolean(config.baseUrl);
+}