Filter dispatch notes by tag

[jongio]

Users who tag sessions still have to scan all notes when they only want annotations for one workflow.

Let dispatch notes list accept --tag <name> and show notes only for sessions with that tag.

Acceptance criteria:

• dispatch notes list --tag bug filters noted sessions by tag.
• dispatch notes --tag bug --json returns the same filtered set in JSON.
• Unknown or empty tags return an empty notes list without error.
• Tests cover text and JSON output with a tag filter.