feat(api): add API documentation and ShareX integration

- Add an API documentation page with curl and ShareX examples.
- Implement a dynamic ShareX configuration endpoint (`/api/v1/sharex/warpbox-anonymous.sxcu`) that generates a `.sxcu` file pre-configured with the instance's base URL.
- Update anonymous uploads to return a private management link (`manageUrl`) and a deletion link (`deleteUrl`) in JSON responses.
- Update README with details on Stage 3 Anonymous Integrations.
- Add styling for the new API documentation view and management details.

backend/libs/handlers/manage.go

@@ -0,0 +1,87 @@
+package handlers
+
+import (
+	"net/http"
+
+	"warpbox.dev/backend/libs/helpers"
+	"warpbox.dev/backend/libs/services"
+	"warpbox.dev/backend/libs/web"
+)
+
+type managePageData struct {
+	Box             boxView
+	Token           string
+	FileCount       int
+	TotalSize       string
+	ExpiresLabel    string
+	DownloadCount   int
+	MaxDownloads    int
+	Protected       bool
+	DeleteActionURL string
+}
+
+func (a *App) ManageBox(w http.ResponseWriter, r *http.Request) {
+	box, ok := a.loadManagedBox(w, r)
+	if !ok {
+		return
+	}
+
+	a.renderer.Render(w, http.StatusOK, "manage.html", web.PageData{
+		Title:       "Manage upload",
+		Description: "Delete this anonymous Warpbox upload.",
+		Data:        a.managePageData(box, r.PathValue("token")),
+	})
+}
+
+func (a *App) ManageDeleteBox(w http.ResponseWriter, r *http.Request) {
+	box, ok := a.loadManagedBox(w, r)
+	if !ok {
+		return
+	}
+
+	if err := a.uploadService.DeleteBoxWithToken(box.ID, r.PathValue("token")); err != nil {
+		a.logger.Warn("anonymous delete failed", "source", "anonymous-delete", "severity", "warn", "code", 4102, "box_id", box.ID, "error", err.Error())
+		http.NotFound(w, r)
+		return
+	}
+	http.Redirect(w, r, "/d/"+box.ID+"/deleted", http.StatusSeeOther)
+}
+
+func (a *App) ManageDeleted(w http.ResponseWriter, r *http.Request) {
+	a.renderer.Render(w, http.StatusOK, "manage_deleted.html", web.PageData{
+		Title:       "Upload deleted",
+		Description: "This Warpbox upload has been deleted.",
+		Data:        boxView{ID: r.PathValue("boxID")},
+	})
+}
+
+func (a *App) loadManagedBox(w http.ResponseWriter, r *http.Request) (services.Box, bool) {
+	box, err := a.uploadService.GetBox(r.PathValue("boxID"))
+	if err != nil {
+		http.NotFound(w, r)
+		return services.Box{}, false
+	}
+	if !a.uploadService.VerifyDeleteToken(box, r.PathValue("token")) {
+		http.NotFound(w, r)
+		return services.Box{}, false
+	}
+	return box, true
+}
+
+func (a *App) managePageData(box services.Box, token string) managePageData {
+	var totalSize int64
+	for _, file := range box.Files {
+		totalSize += file.Size
+	}
+	return managePageData{
+		Box:             boxView{ID: box.ID},
+		Token:           token,
+		FileCount:       len(box.Files),
+		TotalSize:       helpers.FormatBytes(totalSize),
+		ExpiresLabel:    box.ExpiresAt.Format("Jan 2, 2006 15:04 MST"),
+		DownloadCount:   box.DownloadCount,
+		MaxDownloads:    box.MaxDownloads,
+		Protected:       a.uploadService.IsProtected(box),
+		DeleteActionURL: "/d/" + box.ID + "/manage/" + token + "/delete",
+	}
+}