Problem: `nix fmt -- --check .` fails because treefmt uses `--ci`
not `--check`. `bug_report.yaml` had a pre-existing prettier issue.
Solution: use `--ci` flag for treefmt, format `bug_report.yaml`.
Problem: vimdoc did not document per-forge feature differences or
the new capabilities field on the forge interface.
Solution: add COMPATIBILITY section with per-forge feature matrix,
document `capabilities` in the `forge.Forge` interface fields, and
update the source skeleton example.
Problem: forge.nvim silently ignored unsupported features on
non-GitHub forges. Codeberg `pr_for_branch_cmd` blocked all PR
creation, CI picker had zero actions, `repo_info` was hardcoded,
and the compose buffer showed draft/reviewer fields that did nothing.
Solution: add `forge.Capabilities` declaration (`draft`, `reviewers`,
`per_pr_checks`, `ci_json`) to each source. Compose buffer hides
unsupported fields. Per-PR checks falls back to repo-wide CI with
a notification. Fix Codeberg `pr_for_branch_cmd` to filter by branch
via jq, implement `repo_info` and `list_runs_json_cmd` via Gitea API,
add `default_branch_cmd` fallback, and add yank notifications for
GitLab/Codeberg.