dsh-session-trash-90d: Add a session recycle bin to the DSH Web GUI

DSH 0.2.x lacks an API for deleting sessions, and manually deleted files are resurrected by the host's memory write-back mechanism. `full626/dsh-session-trash-90d` resolves this issue by using a "tombstone" approach combined with "startup replay." It provides a 90-day recycle bin, original workspace recovery, and archive cancellation. This article explains its working mechanism, installation commands, verification scripts, and usage notes.