fix: honor positional input in save commands

[4paulpak]

Closes #645

This fixes non-interactive positional input handling for draft save commands.

Changes:

• message save now uses the positional message when it is provided, even when stdin is not a TTY
• template save now uses the positional template when it is provided, even when stdin is not a TTY
• template save no longer appends the same draft twice

Repro before:

• message save ... $'Subject: ...\r\n\r\nBody' sent APPEND Drafts {0}
• template save ... $'From: ...\n\nBody' failed with cannot parse template

Verified with patched binary against IMAP proxy:

• message save now sends a non-empty append (APPEND Drafts {71} in my repro)
• template save now sends a non-empty append (APPEND Drafts {347} in my repro)