feat: make /transfer bidirectional across telegram and tui

README.md

@@ -486,7 +486,7 @@ pnpm tui:fs
 | `/verbose` | Toggle verbose output mode |
 | `/pair` | Generate/list/revoke DM pairing codes |
 | `/fullscreen` | Switch to fullscreen mode |
-| `/transfer <dest>` | Transfer session to another frontend |
+| `/transfer <dest>` | Transfer session to another frontend (`telegram` or `tui`) |
 | `/quit` | Exit |
 
 #### Runtime Model Switching
@@ -1476,7 +1476,7 @@ Exit code is `1` if any check fails, `0` otherwise. Checks that depend on a vali
 - Sessions persist in `~/.local/share/flynn/sessions.db`
 - Session ID format: `{frontend}:{userId}` (e.g., `telegram:123456789`)
 - History survives restarts
-- Transfer sessions between frontends with `/transfer`
+- Transfer sessions between frontends with `/transfer <telegram|tui>`
 
 ## Architecture