feat: add emoji reaction support for files

- Implement `ReactionService` to manage file reactions in the database.
- Add `POST /d/{boxID}/f/{fileID}/react` endpoint to handle user reactions.
- Add `GET /emoji/{pack}/{file}` endpoint to serve custom emoji assets.
- Support loading custom emoji packs dynamically from the data directory.
- Update README with instructions on configuring emoji reaction packs.

backend/libs/httpserver/server.go

@@ -32,13 +32,18 @@ func New(cfg config.Config, logger *slog.Logger) (*http.Server, error) {
 		uploadService.Close()
 		return nil, err
 	}
+	reactionService, err := services.NewReactionService(uploadService.DB())
+	if err != nil {
+		uploadService.Close()
+		return nil, err
+	}
 	banService, err := services.NewBanService(uploadService.DB())
 	if err != nil {
 		uploadService.Close()
 		return nil, err
 	}
 	stopJobs := jobs.StartAll(cfg, logger, uploadService, banService)
-	app := handlers.NewApp(cfg, logger, renderer, uploadService, authService, settingsService, banService)
+	app := handlers.NewApp(cfg, logger, renderer, uploadService, authService, settingsService, reactionService, banService)
 
 	router := http.NewServeMux()
 	app.RegisterRoutes(router)