feat: add knowledge directory management for documents and FAQs

- Implemented directory validation in Create and Update knowledge document services.
- Added directory selection in document and FAQ edit dialogs with a new KnowledgeDirectoryPanel component.
- Enhanced API to support fetching, creating, updating, and deleting knowledge directories.
- Updated data models to include directory information for knowledge documents and FAQs.
- Added translations for directory-related messages in English and Chinese.

web/messages/en-US.json

@@ -1781,6 +1781,13 @@
     "baseSaveFailed": "Could not save the knowledge base.",
     "baseDeleted": "Knowledge base deleted: {name}",
     "baseDeleteFailed": "Could not delete the knowledge base.",
+    "loadDirectoriesFailed": "Could not load directories.",
+    "directoryCreated": "Directory created: {name}",
+    "directoryUpdated": "Directory updated: {name}",
+    "directoryDeleted": "Directory deleted: {name}",
+    "directorySaveFailed": "Could not save the directory.",
+    "directoryDeleteFailed": "Could not delete the directory.",
+    "directoryNameRequired": "Directory name is required.",
     "rebuildStarted": "Knowledge base reindex started: {name}",
     "rebuildFailed": "Could not rebuild the knowledge base index.",
     "sortUpdated": "Knowledge base order updated.",
@@ -1791,6 +1798,21 @@
     "rebuildIndex": "Rebuild Index",
     "deleting": "Deleting...",
     "delete": "Delete",
+    "directory": "Directory",
+    "allContent": "All content",
+    "rootContent": "Root content",
+    "rootDirectory": "Root directory",
+    "parentDirectory": "Parent directory",
+    "createDirectory": "New directory",
+    "createSubDirectory": "New subdirectory",
+    "editDirectory": "Edit directory",
+    "expandDirectory": "Expand directory",
+    "collapseDirectory": "Collapse directory",
+    "selectDirectory": "Select directory",
+    "searchDirectory": "Search directories",
+    "emptyDirectory": "No matching directories",
+    "directoryName": "Directory name",
+    "directoryNamePlaceholder": "Enter directory name",
     "searchBase": "Search knowledge bases",
     "query": "Search",
     "emptyBases": "No matching knowledge bases",