amnesic

Leave out names in saved summaries; set folder times back; more warnings

- A summary saved after encrypting or decrypting is now named
  encryption-summary.txt or decryption-summary.txt, and every file name
  and path in it is replaced with "…". The report on screen is unchanged.
- Encrypt and decrypt record the modified times of the folders they write
  in (the input's, the output's and the current one) and set them back
  when they finish. Folders the run didn't change are left alone.
- The key screen warns that selecting the key to copy it puts it on the
  clipboard, where clipboard history keeps a copy.
- In iTerm2, the exit prompt notes that its "save lines to scrollback"
  setting would keep what the screen showed.
- On a Mac with FileVault off (asked of `fdesetup status`), the
  copy-on-write warning says the old contents are readable and how to
  turn it on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TMPqvgKfc66hdUaU8TRa74