feat(accounts): implement user accounts, sessions, and dashboards

Introduce Stage 4 features to support multi-user accounts, cookie-based web sessions, and personal dashboards.

Changes include:
- Adding `/register` to bootstrap the first admin account and `/login`/`/logout` for session management.
- Creating a personal dashboard (`/app`) to display owned boxes, storage usage, and upload history.
- Implementing admin user management (`/admin/users`) for generating invite links and managing user states.
- Updating the bbolt database schema to store users, sessions, invites, and collections.
- Adding `golang.org/x/crypto` for password hashing and introducing unit tests for account handlers.

backend/libs/handlers/upload.go

@@ -14,18 +14,39 @@ import (
 )
 
 func (a *App) Upload(w http.ResponseWriter, r *http.Request) {
-	r.Body = http.MaxBytesReader(w, r.Body, a.uploadService.MaxUploadSize()*8)
-	if err := r.ParseMultipartForm(a.uploadService.MaxUploadSize() * 8); err != nil {
+	user, loggedIn := a.currentUser(r)
+	isAdminUpload := loggedIn && user.Role == services.UserRoleAdmin
+	if !isAdminUpload {
+		r.Body = http.MaxBytesReader(w, r.Body, a.uploadService.MaxUploadSize()*8)
+	}
+	parseLimit := a.uploadService.MaxUploadSize() * 8
+	if isAdminUpload {
+		parseLimit = 32 << 20
+	}
+	if err := r.ParseMultipartForm(parseLimit); err != nil {
 		helpers.WriteJSONError(w, http.StatusBadRequest, "upload form could not be read")
 		return
 	}
 
 	files := uploadFiles(r)
+	var ownerID string
+	var collectionID string
+	if loggedIn {
+		ownerID = user.ID
+		collectionID = r.FormValue("collection_id")
+		if !a.authService.CollectionOwnedBy(collectionID, user.ID) {
+			helpers.WriteJSONError(w, http.StatusForbidden, "collection not found")
+			return
+		}
+	}
 	result, err := a.uploadService.CreateBox(files, services.UploadOptions{
 		MaxDays:           parseInt(r.FormValue("max_days")),
 		MaxDownloads:      parseInt(r.FormValue("max_downloads")),
 		Password:          r.FormValue("password"),
 		ObfuscateMetadata: r.FormValue("obfuscate_metadata") == "on",
+		OwnerID:           ownerID,
+		CollectionID:      collectionID,
+		SkipSizeLimit:     isAdminUpload,
 	})
 	if err != nil {
 		a.logger.Warn("upload failed", "source", "user-upload", "severity", "warn", "code", 4001, "error", err.Error())