v6.0 release tracking

Tracking issue for changes planned for the next major release of `@diplodoc/cli` (v6.0).

## Scope

This issue is the single source of truth for breaking-change candidates and proposals that should land together with the v6.0 release. Anything labelled [`major`](https://github.com/diplodoc-platform/cli/issues?q=is%3Aopen+label%3Amajor) is a candidate; this issue summarises the current state.

## How to add a candidate

1. Open a new issue describing the proposed change and its motivation.
2. Apply the `major` label.
3. Add a checklist entry below referencing the issue/PR.

## Candidates

- [ ] #1900 — make `GenericIncluder` `linkIndexAutotitle` behavior the default
- [ ] #1902 — make `GenericIncluder` `orderBy: natural` the default
- [ ] We fix the build-manifest as a non‑disabling build element.

## Live filters

- Open candidates: https://github.com/diplodoc-platform/cli/issues?q=is%3Aopen+label%3Amajor
- Merged/closed candidates: https://github.com/diplodoc-platform/cli/issues?q=is%3Aclosed+label%3Amajor

## Out of scope

Additive, backward-compatible changes (new opt-in options, new commands, etc.) do not need to wait for v6 and should land in regular minor/patch releases.