feat(oo): file deep links, login check, replace-in (fresh upload)

- link: print Products/Files/DocEditor.aspx?fileid=… deep links (title+url)
- lib: FileEditorURL/FolderURL helpers (+tests)
- users check: verify credentials (userName vs email) via authentication.json
- projects files replace-in FOLDER_ID FILE...: hard delete same stem|ext in a
  folder + fresh upload → single clean version (no version history)

links.go

@@ -0,0 +1,37 @@
+package onlyoffice
+
+// Deep links to OnlyOffice portal objects.
+
+import (
+	"fmt"
+	"net/url"
+	"strings"
+)
+
+// FileEditorURL builds the OnlyOffice DocEditor deep link for a portal file id:
+//
+//	https://<portal>/Products/Files/DocEditor.aspx?fileid=<id>
+//
+// portalBase may include a trailing slash; fileID is trimmed and URL-escaped.
+func FileEditorURL(portalBase, fileID string) string {
+	base := strings.TrimRight(strings.TrimSpace(portalBase), "/")
+	return fmt.Sprintf("%s/Products/Files/DocEditor.aspx?fileid=%s",
+		base, url.QueryEscape(strings.TrimSpace(fileID)))
+}
+
+// FileEditorURL is the client-bound convenience wrapper (uses the portal URL
+// the client was built with).
+func (c *Client) FileEditorURL(fileID string) string {
+	return FileEditorURL(c.baseURL(), fileID)
+}
+
+// FolderURL builds a Documents-folder deep link for a folder id.
+func FolderURL(portalBase, folderID string) string {
+	base := strings.TrimRight(strings.TrimSpace(portalBase), "/")
+	return fmt.Sprintf("%s/Products/Files/Default.aspx#folder=%s", base, url.QueryEscape(strings.TrimSpace(folderID)))
+}
+
+// FolderURL is the client-bound convenience wrapper.
+func (c *Client) FolderURL(folderID string) string {
+	return FolderURL(c.baseURL(), folderID)
+}