[emaarco]

Summary

Contributors could not see how a command gets from the terminal into the domain model, or how the hexagonal layout of src/ is meant to work. This PR adds a page that shows it and tidies the docs navigation.

• New page docs/architecture.md in a new sidebar group "Contributing". It starts with the hexagon and the import rules that test/architecture.test.ts checks. Its core is the journey of bpmn add: a compact diagram of eight numbered stops, one class each, with one colour per layer. A short section per stop follows, with the file and the real code that hands over to the next stop, and at the end how bpmn apply, mutateFile() and applyToXml() differ. Finally, the command definitions and what a new command needs. "Where new code goes" links to CONTRIBUTING.md instead of repeating it. Three reader personas (new contributor, maintainer, library user) reviewed an earlier draft, and their findings are worked in.
• "Ids, kinds and keys" becomes "Syntax and output" and moves under "Using the CLI", next to Commands. The separate "Reference" group and nav entry are removed. The URL /reference stays, so links from the README keep working. Link texts in commands.md, contract.md and the README follow the new title.
• Docs kit vendored at 1.26.0 (Miragon/corporate-identity#63). A click on an image or a Mermaid diagram opens it full screen, and <div data-zoom> opens anything else the same way. The CI checkout of corporate-identity moves from v1.10.0 to v1.26.0, as the comment next to it asks.

Checklist

• npm run typecheck passes
• npm run gate passes
• src/report/guide.ts and the matching page in docs/ are updated (only if a command, option or output changed)
• PR title is a changelog-worthy Conventional-Commit summary

Also checked: npm run docs:build passes, check:kit reports "Kit 1.26.0: 14 Dateien unverändert.", and all diagrams render without Mermaid errors. The overlay was checked in a browser in light and dark mode.

Linked issue

None.