[fohara]

Cuts 0.3.1: version bump, changelog section, lockfile.

Two fixes landed since 0.3.0, both on the Markdown write path and both the
same root cause the 0.3.0 sweep left standing. The parsed model does not record
a task's free-text body, and add and format each assumed a task was its
checkbox line plus its annotation block.

• fix(add): stop inserting a task between the previous task's title and its body #49 lash add inserted between the previous task's title and its body, which
  reassigned that body to a task it had nothing to do with. Present since 0.1.0,
  reported from real use in flawd's tasks/tasks.polish.md.
• fix(format): stop deleting task bodies and everything else inside ## Tasks #50 lash format deleted everything inside ## Tasks it could not rebuild
  from the task tree: bodies, --- separators, comments, ### Subsection
  headings, and the continuation lines of wrapped contextual notes. The README
  tells people to run format.

Patch rather than minor. Both are bug fixes, and the one behaviour change,
blank lines between tasks now surviving format, is a formatting nuance rather
than a break in the format or the CLI.

Local checks before pushing: cargo fmt --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace --all-targets (494
passing), cargo test --doc.

After merge: tag v0.3.1 and push it. cargo-dist builds the binaries, writes
the release notes from the changelog section, and publishes the Homebrew
formula.