v0.13.0

New: trck changelog — release notes from the tracker

trck changelog --since <DATE|TIMESTAMP> prints, as nested markdown, the
issues completed since a cutoff — turning the tracker into a changelog source.
Paired with a release's timestamp (precise since v0.12.0), it answers "what
shipped since the last release?".

$ trck changelog --since 2026-06-10
## Shipped since 2026-06-10 — 18 issues

- #058 deps: shorter edges / fewer crossings in the graph layout (deps)
- #048 Free-form custom fields: set/filter/sort arbitrary key→value (cli)
  - #049 set: --field/--unset to write/clear free-form custom fields (cli)
  ...

• Selects issues closed in a terminal status on/after --since (inclusive),
  excluding wontfix/duplicate/superseded.
• All kinds included; children nest under their shipped parent (an issue
  whose parent is outside the window renders at the top level).
• Sorted newest-closed-first, under a ## Shipped since … — N issues header.
• --since accepts a bare date (2026-06-10) or a full timestamp
  (2026-06-10T14:00:00Z).