73085e6e69
Issue 1600 asks for full rename UX: set a custom title, remove it back to `(unnamed)`. The set side already shipped as `deepseek thread set-name <id> <name>`, but there was no inverse — users who wanted to drop a no-longer-relevant title had to either edit the SQLite store by hand or set a placeholder string. Add `deepseek thread clear-name <id>`, mirroring the existing `SetName` arm in `run_thread_command`: look up the thread, set `name = None`, refresh `updated_at`, upsert. Printed confirmation is `cleared name for <id>` so it stays distinguishable from the `renamed` line emitted by `set-name`. Snapshot help test and the parser-matrix test both gain the new subcommand. No state-store changes: `upsert_thread` already accepts `name: None` and `thread list` already prints `(unnamed)` when the field is empty, so the round-trip is complete with this CLI-only change. Co-authored-by: Claude <noreply@anthropic.com>