[6.x] Implement approval workflows

[riasvdv]

Description

Adds configurable approval workflows for draft publishing, including user-review stages, carried approvals, per-group requirements, review notifications, workflow activity history, and CP review controls.

See Workflows

Workflow management

Review stages

[linear-code]

CMS-2330

[github-actions]

📚 Storybook previews

@craftcms/ui — open Storybook

Changed components:

• Components/Button
• Components/Button
• Components/Timeline Item

resources/js — open Storybook

No changed components detected in this Storybook.

[github-actions]

This PR had conflicts with 6.x. Claude attempted an automatic resolution and pushed a merge commit. Please review the merge commit carefully before approving/merging.

Claude's response

Merge resolved, committed, and pushed.

Summary

Only one file conflicted: src/Cp/Settings.php, in the control panel settings nav builder.

The conflict: both sides inserted a new entry into the "Content" section between "Entry Types" and "Fields". This branch (94886ab on 6.x moved "Assets" there, relocating it out of its own "Media" section; commit 7399780 on this branch added a Pro-edition-gated "Workflows" entry in the same position.

Resolution: these are independent additions, so both were kept. "Assets" sits directly after "Entry Types" (preserving 6.x's restructured ordering exactly), followed by the Pro-gated "Workflows" block, then "Fields". The 6.x removal of the separate "Media" section auto-merged cleanly and was left as-is, and the Edition import added by this branch survived intact.

Needs a look: the relative ordering of "Assets" vs "Workflows" is the one genuinely ambiguous bit — each side placed its own item immediately after "Entry Types", so neither expressed an opinion about the other. I took the conservative reading that keeps 6.x's nav order unbroken and left a // CONFLICT-REVIEW: comment at that spot; if "Workflows" is meant to sit higher in the Content nav, it's a one-block move.

Verified: no conflict markers remain anywhere in the repo, php -l passes on the file, and no unmerged paths are left. I could not run Pint or the test suite — vendor/ is not installed in this checkout — so CI is the first real check on formatting and tests/Unit/Cp/SettingsTest.php (which does not currently assert on nav ordering).