feat(cli): add-all command and auto_delete_added_files config

[sebastianbraun25]

Problem

The openkb add command supports adding directories recursively, but users who frequently download documents to /raw must manually invoke openkb add raw/ and then manually delete processed files. There is no batch processing command for the /raw staging directory, and no configuration option to auto-delete successfully ingested files and duplicates.

Solution

• Add new config parameter auto_delete_added_files (default: false)
• Implement add-all CLI command that processes all files in /raw directory
• Apply auto-delete logic to both add and add-all commands (when config is enabled)
• Delete files on both success ("added") and duplicates ("skipped") to keep raw/ clean
• Preserve failed files to allow user retries
• Update help texts and documentation