Inject the current user's SSH public key into the Debian seed ISO

user-data is now a template with an @SSH_PUBKEY@ placeholder that
build-seed.sh fills in from SSH_PUBKEY_FILE, ~/.ssh/id_*.pub or ssh-agent.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

seediso/debian13/user-data

@@ -11,7 +11,7 @@ users:
     sudo: "ALL=(ALL) NOPASSWD: ALL"
     lock_passwd: false
     ssh_authorized_keys:
-      - ssh-rsa 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 guofang@GUOFANG-OFFICE
+      - @SSH_PUBKEY@
     hashed_passwd: $6$0NtCERV3eO12t9oJ$nlFE2sSc66nFfuD5X0xMnOla1cuzOnHfeGNRY5X7dCDHg.WzWVmuRe7M17Puj44.eCWLnJAWt4WNjd9vP9X0D0
 
 chpasswd: