feat(launcher): implement modpack manifest API endpoint

internal/api/launcher_handler.go

@@ -0,0 +1,37 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"gitea.mrixs.me/minecraft-platform/backend/internal/database"
+	"github.com/go-chi/chi/v5"
+	"github.com/jackc/pgx/v5"
+)
+
+type LauncherHandler struct {
+	ModpackRepo *database.ModpackRepository
+}
+
+func (h *LauncherHandler) GetModpackManifest(w http.ResponseWriter, r *http.Request) {
+	modpackName := chi.URLParam(r, "name")
+	if modpackName == "" {
+		http.Error(w, "Modpack name is required", http.StatusBadRequest)
+		return
+	}
+
+	manifest, err := h.ModpackRepo.GetModpackManifest(r.Context(), modpackName)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			http.Error(w, "Modpack not found or not active", http.StatusNotFound)
+			return
+		}
+		http.Error(w, "Failed to get modpack manifest", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	json.NewEncoder(w).Encode(manifest)
+}