Add SABnzbd client and Downloads view (M4)

SABnzbd client (queue, history, pause/resume, delete, retry) with lenient
number decoding and API-key-safe errors. Downloads view polls while
visible, shows queue and history, and supports pause, delete (with
confirmation) and retry. Add dev/ with pinned Radarr/Sonarr/SABnzbd
containers wired together for manual testing.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/sabnzbd/sabnzbd_test.go

@@ -0,0 +1,124 @@
+package sabnzbd
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+const queueJSON = `{"queue":{"status":"Downloading","paused":false,"kbpersec":"1536.50","speedlimit_abs":"0",
+ "size":"4.0 GB","sizeleft":"2.0 GB","timeleft":"0:21:10","noofslots_total":2,
+ "slots":[
+  {"nzo_id":"SABnzbd_nzo_a","filename":"Movie.2020.1080p","cat":"radarr","status":"Downloading","priority":"Normal",
+   "size":"3 GB","sizeleft":"1 GB","mb":"3072.00","mbleft":"1024.00","percentage":"67","timeleft":"0:11:10"},
+  {"nzo_id":"SABnzbd_nzo_b","filename":"Show.S01E01","cat":"sonarr","status":"Queued","mb":1000,"mbleft":1000,"percentage":0}
+ ]}}`
+
+func newTestClient(t *testing.T, h http.HandlerFunc) *Client {
+	t.Helper()
+	srv := httptest.NewServer(h)
+	t.Cleanup(srv.Close)
+	return NewClient(srv.URL, "secret")
+}
+
+func TestQueue(t *testing.T) {
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		q := r.URL.Query()
+		if q.Get("mode") != "queue" || q.Get("apikey") != "secret" || q.Get("output") != "json" {
+			t.Errorf("unexpected request %s", r.URL)
+		}
+		w.Write([]byte(queueJSON))
+	})
+	q, err := c.Queue(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if q.Paused || q.KBPerSec != 1536.5 || q.TotalSlots != 2 || len(q.Slots) != 2 {
+		t.Fatalf("queue = %+v", q)
+	}
+	s := q.Slots[0]
+	if s.ID != "SABnzbd_nzo_a" || s.Percentage != 67 || s.MB != 3072 || s.Category != "radarr" {
+		t.Errorf("slot = %+v", s)
+	}
+	if q.Slots[1].Percentage != 0 || q.Slots[1].MB != 1000 {
+		t.Errorf("numeric (non-string) values not decoded: %+v", q.Slots[1])
+	}
+}
+
+func TestHistory(t *testing.T) {
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Query().Get("mode") != "history" || r.URL.Query().Get("limit") != "10" {
+			t.Errorf("unexpected request %s", r.URL)
+		}
+		w.Write([]byte(`{"history":{"slots":[
+		 {"nzo_id":"a","name":"Good","status":"Completed","size":"1 GB","completed":1700000000},
+		 {"nzo_id":"b","name":"Bad","status":"Failed","fail_message":"Aborted, cannot be completed"}]}}`))
+	})
+	h, err := c.History(context.Background(), 10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(h) != 2 || h[0].Failed() || !h[1].Failed() || h[1].FailMessage == "" {
+		t.Fatalf("history = %+v", h)
+	}
+}
+
+func TestActions(t *testing.T) {
+	var got []string
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		q := r.URL.Query()
+		got = append(got, strings.Join([]string{q.Get("mode"), q.Get("name"), q.Get("value"), q.Get("del_files")}, "|"))
+		w.Write([]byte(`{"status":true}`))
+	})
+	ctx := context.Background()
+	for _, err := range []error{
+		c.Pause(ctx), c.Resume(ctx),
+		c.DeleteJob(ctx, "id1", true), c.DeleteHistory(ctx, "id2", false), c.Retry(ctx, "id3"),
+	} {
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	want := []string{"pause|||", "resume|||", "queue|delete|id1|1", "history|delete|id2|0", "retry||id3|"}
+	if strings.Join(got, ",") != strings.Join(want, ",") {
+		t.Errorf("requests = %v, want %v", got, want)
+	}
+}
+
+func TestErrors(t *testing.T) {
+	tests := map[string]struct {
+		status int
+		body   string
+		want   string
+	}{
+		"bad key":      {200, `{"status":false,"error":"API Key Incorrect"}`, "API Key Incorrect"},
+		"host check":   {200, `Access denied - Hostname verification failed`, "Hostname verification failed"},
+		"http error":   {500, `boom`, "HTTP 500: boom"},
+		"status false": {200, `{"status":false}`, "request failed"},
+	}
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(tc.status)
+				w.Write([]byte(tc.body))
+			})
+			_, err := c.Version(context.Background())
+			if err == nil || !strings.Contains(err.Error(), tc.want) {
+				t.Fatalf("err = %v, want containing %q", err, tc.want)
+			}
+		})
+	}
+}
+
+func TestTransportErrorHidesAPIKey(t *testing.T) {
+	c := NewClient("http://127.0.0.1:1", "topsecretkey")
+	_, err := c.Version(context.Background())
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	if strings.Contains(err.Error(), "topsecretkey") {
+		t.Errorf("error leaks API key: %v", err)
+	}
+}