feat(llm): add LLM integration instructions and handler

* Serve LLM instructions at `/llm`
* Include markdown content for memory instructions
* Update README with LLM integration details
* Add tests for LLM instructions handler
* Modify database migrations to use GUIDs for thoughts and projects

internal/app/llm_test.go

@@ -0,0 +1,29 @@
+package app
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	amcsllm "git.warky.dev/wdevs/amcs/llm"
+)
+
+func TestServeLLMInstructions(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/llm", nil)
+	rec := httptest.NewRecorder()
+
+	serveLLMInstructions(rec, req)
+
+	res := rec.Result()
+	defer res.Body.Close()
+
+	if res.StatusCode != http.StatusOK {
+		t.Fatalf("status = %d, want %d", res.StatusCode, http.StatusOK)
+	}
+	if got := res.Header.Get("Content-Type"); got != "text/markdown; charset=utf-8" {
+		t.Fatalf("content-type = %q, want %q", got, "text/markdown; charset=utf-8")
+	}
+	if body := rec.Body.String(); body != string(amcsllm.MemoryInstructions) {
+		t.Fatalf("body = %q, want embedded instructions", body)
+	}
+}