feat: implement dynamic server list loading from API

Add internal/api package to fetch server list from /api/servers.json endpoint

Replace hardcoded server list with dynamic API call

Implement loading states, error handling, and refresh capability

internal/api/server_test.go

@@ -0,0 +1,133 @@
+// package api handles launcher-specific API calls to the backend.
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/screens"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFetchServerList_Success(t *testing.T) {
+	// Arrange - create mock server response
+	serverResp := ServerResponse{
+		Servers: []ServerInfo{
+			{Slug: "hitech", Name: "HiTech 1.21", Version: "1.21", IP: "192.168.1.100"},
+			{Slug: "vanilla", Name: "Vanilla 1.20", Version: "1.20", IP: "192.168.1.101"},
+		},
+	}
+
+	// Create test server with mock response
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/servers.json" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.Method != http.MethodGet {
+			t.Errorf("unexpected method: %s", r.Method)
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(serverResp)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.NoError(t, err)
+
+	// Assert - check results
+	require.Len(t, modpacks, 2)
+	require.Equal(t, screens.Modpack{Slug: "hitech", Name: "HiTech 1.21"}, modpacks[0])
+	require.Equal(t, screens.Modpack{Slug: "vanilla", Name: "Vanilla 1.20"}, modpacks[1])
+}
+
+func TestFetchServerList_EmptyList(t *testing.T) {
+	// Arrange - create mock server with empty servers list
+	serverResp := ServerResponse{Servers: []ServerInfo{}}
+
+	// Create test server with mock response
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/servers.json" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.Method != http.MethodGet {
+			t.Errorf("unexpected method: %s", r.Method)
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(serverResp)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.NoError(t, err)
+
+	// Assert - should return empty slice
+	require.Empty(t, modpacks)
+}
+
+func TestFetchServerList_NetworkError(t *testing.T) {
+	// Act - call FetchServerList with invalid URL that will fail to connect
+	modpacks, err := FetchServerList("http://localhost:12345/api/servers.json") // Assuming no server on this port
+
+	// Assert - should return error
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "making request")
+}
+
+func TestFetchServerList_HTTPError(t *testing.T) {
+	// Arrange - create test server that returns 500 error
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "unexpected status code: 500")
+}
+
+func TestFetchServerList_InvalidJSON(t *testing.T) {
+	// Arrange - create test server that returns invalid JSON
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"invalid": json}`))
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "decoding JSON")
+}
+
+func TestFetchServerList_Timeout(t *testing.T) {
+	// Arrange - create test server that delays response to trigger timeout
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Sleep longer than our timeout to trigger timeout error
+		time.Sleep(15 * time.Second)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "context deadline exceeded")
+	require.Contains(t, err.Error(), "making request")
+}