fix: fetch both sub and dub streams on watch page load

Previously the backend only fetched streams for the single requested
mode (defaulting to sub), so modeSources never had a dub entry.
The frontend's switchMode showed visual feedback but streamUrlForMode
returned an empty string since no dub token existed.
Now both modes are fetched and availableModes is derived from what
actually resolved.

internal/playback/service/service.go

@@ -126,19 +126,63 @@ func (s *playbackService) BuildWatchData(ctx context.Context, animeID int, title
 		}
 	}
 
+	type SubtitleItem struct {
+		Lang    string `json:"lang"`
+		URL     string `json:"url,omitempty"`
+		Referer string `json:"referer,omitempty"`
+		Token   string `json:"token"`
+	}
+
+	type ModeSource struct {
+		URL       string         `json:"url,omitempty"`
+		Referer   string         `json:"referer,omitempty"`
+		Token     string         `json:"token"`
+		Subtitles []SubtitleItem `json:"subtitles"`
+		Qualities []string       `json:"qualities,omitempty"`
+	}
+
+	modeSources := map[string]ModeSource{}
 	var result *domain.StreamResult
-	for _, p := range s.providers {
-		res, err := p.GetStreams(ctx, animeID, searchTitles, episode, mode)
-		if err == nil && res != nil {
-			result = res
+
+	for _, m := range []string{"sub", "dub"} {
+		for _, p := range s.providers {
+			res, err := p.GetStreams(ctx, animeID, searchTitles, episode, m)
+			if err != nil || res == nil {
+				continue
+			}
+
+			var subItems []SubtitleItem
+			for _, sub := range res.Subtitles {
+				subToken, _ := s.SignProxyToken(sub.URL, res.Referer, "subtitle")
+				subItems = append(subItems, SubtitleItem{
+					Lang:  sub.Label,
+					Token: subToken,
+				})
+			}
+
+			streamToken, _ := s.SignProxyToken(res.URL, res.Referer, "stream")
+			modeSources[m] = ModeSource{
+				URL:       res.URL,
+				Referer:   res.Referer,
+				Token:     streamToken,
+				Subtitles: subItems,
+			}
+
+			if m == mode {
+				result = res
+			}
 			break
 		}
 	}
 
-	if result == nil {
+	if len(modeSources) == 0 {
 		return nil, fmt.Errorf("no streams found")
 	}
 
+	if result == nil {
+		return nil, fmt.Errorf("no streams found for mode %s", mode)
+	}
+
 	// 3. Get start time from progress
 	startTime := 0.0
 	var watchlistStatus string
@@ -193,8 +237,6 @@ func (s *playbackService) BuildWatchData(ctx context.Context, animeID int, title
 	}
 
 	// 5. Build provider data
-	// AllAnime currently returns one stream in result.URL
-	// We wrap it for the template
 	streams := []domain.ProviderStream{
 		{
 			Name:      "Primary",
@@ -205,41 +247,6 @@ func (s *playbackService) BuildWatchData(ctx context.Context, animeID int, title
 		},
 	}
 
-	type SubtitleItem struct {
-		Lang    string `json:"lang"`
-		URL     string `json:"url,omitempty"`
-		Referer string `json:"referer,omitempty"`
-		Token   string `json:"token"`
-	}
-
-	type ModeSource struct {
-		URL       string         `json:"url,omitempty"`
-		Referer   string         `json:"referer,omitempty"`
-		Token     string         `json:"token"`
-		Subtitles []SubtitleItem `json:"subtitles"`
-		Qualities []string       `json:"qualities,omitempty"`
-	}
-
-	var subtitleItems []SubtitleItem
-	for _, sub := range result.Subtitles {
-		subToken, _ := s.SignProxyToken(sub.URL, result.Referer, "subtitle")
-		subtitleItems = append(subtitleItems, SubtitleItem{
-			Lang:  sub.Label,
-			Token: subToken,
-		})
-	}
-
-	token, _ := s.SignProxyToken(result.URL, result.Referer, "stream")
-
-	modeSources := map[string]ModeSource{
-		mode: {
-			URL:       result.URL,
-			Referer:   result.Referer,
-			Token:     token,
-			Subtitles: subtitleItems,
-		},
-	}
-
 	go s.warmStreamURL(result.URL, result.Referer)
 
 	// 6. Resolve relations/seasons
@@ -281,7 +288,14 @@ func (s *playbackService) BuildWatchData(ctx context.Context, animeID int, title
 		},
 		"ModeSources":    modeSources,
 		"InitialMode":    mode,
-		"AvailableModes": []string{"sub", "dub"},
+		"AvailableModes": func() []string {
+			var modes []string
+			for m := range modeSources {
+				modes = append(modes, m)
+			}
+			sort.Strings(modes)
+			return modes
+		}(),
 		"Segments":       segments,
 	}