feat(backend): implement HTTP API, auth, chat, and admin surfaces

Expose learning, registration controls, mentor chat, realtime WebSocket, and staff administration.

backend/internal/api/community_test.go

@@ -0,0 +1,31 @@
+package api_test
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestCommunityEndpointPublic(t *testing.T) {
+	e := setup(t)
+	code, body := e.do(t, "GET", "/api/community", "", nil)
+	if code != http.StatusOK {
+		t.Fatalf("community: %d %v", code, body)
+	}
+	don, ok := body["donation"].(map[string]any)
+	if !ok {
+		t.Fatalf("missing donation: %v", body)
+	}
+	if _, ok := don["enabled"]; !ok {
+		t.Fatalf("missing donation.enabled: %v", don)
+	}
+	if don["mode"] != "chat" {
+		t.Fatalf("donation.mode want chat, got %v", don["mode"])
+	}
+	if _, hasCard := don["cardNumber"]; hasCard {
+		t.Fatal("public card number must not be exposed")
+	}
+	// Telegram channel surface was removed from the product.
+	if _, hasChannel := body["channel"]; hasChannel {
+		t.Fatal("legacy channel field must not be exposed")
+	}
+}