Add stdin input for dispatch notes set

[jongio]

Long notes are awkward to pass through shell quoting. dispatch notes set <id> --stdin should read the full note from standard input, preserving newlines, so scripts and editors can write notes directly.

Acceptance criteria:

• dispatch notes set <id> --stdin reads the note from standard input.
• Newlines are preserved in config and in dispatch notes get.
• Existing dispatch notes set <id> <text...> behavior stays unchanged.