feat: share env files as encrypted links

S → f on a repo, an env file or a key in one copies a
lazysecrets://share link holding the env files, encrypted (age) with
a secret's value: whoever can read that secret can open it. The key is
share.key in the repo's .lazysecrets.yaml, else in the config, else
picked when sharing; on Azure the link pins its version. Opening one
says what it holds, decrypts when asked, and saves the files in the
clone of the repo (or a folder chosen), replacing existing ones only
when asked. lazysecrets share prints a link from the command line.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -14,7 +14,8 @@ A terminal UI for finding, reading and sharing secrets. Inspired by the fantasti
   fzf-style matching.
 - **Share links**: Share `lazysecrets://` links with colleagues. A colleague opens it
   with their own access, from the terminal or with a click in the browser
-  or chat.
+  or chat. `.env` files can be shared too, as a link encrypted with a
+  secret your team can read.
 - **Neovim integration**: via [lazysecrets.nvim](https://github.com/karleinarb/lazysecrets.nvim)
 - **Careful with values**: values stay hidden until you reveal them, and
   copied values are cleared from the clipboard after 30 seconds.