#970 Feat(workflow): step cards, a laid-out studio and shared workflows (18/21)

Stack 18/21 · after #969 · next #971 · uses KubeVela kubevela/kubevela#7421 at runtime

Targets main but builds on #969, so the earlier stack commits show here too: review the last commit only. Merge after #969.

Description of your changes

• Runs: steps are status cards laid out by what they wait on; a step waiting for approval can be approved from its card.
• Studio: steps are laid out the same way, added from a + on each card through a short wizard, with a settings panel and drag-to-depend.
• Shared workflows: a workflow can reference a shared Workflow, the project's own or a global one, managed on a new Workflows page.

Fixes #

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run yarn lint to ensure the frontend changes are ready for review.
• Run make reviewableto ensure the server changes are ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

Special notes for your reviewer

• Global workflows live in vela-system and are resolved by KubeVela's workflowRef fallback (kubevela/kubevela#7421).
• The Workflows page lists a picked project's workflows; with "All projects" it shows nothing yet. It should say to pick one; I'll add that here unless you'd rather it list everything.