issue 4531 slice 46: PublishingShell create a site #4959

Parent: #4531

Slice goal

PublishingShell Sites: create a site from the sites list (toolbar and empty state). The empty copy already says to create a site, but there is no action. One confirm creates the site and opens its workspace. Cancel creates nothing.

Out of scope

• Rename, copy, or delete of an existing site (sibling slices)
• UAT sign-off for unified Publishing UI (SC-001 / SC-003 / SC-008) #1371 human UAT
• JSF deep-page deletes
• Delivery-server editor

Acceptance criteria

• Valid name creates a site and selects it
• Cancel and invalid/duplicate names create nothing
• HTTP 400/403/409 stay on the list and do not open a fake workspace
• Vitest plus surface-filtered Playwright
• product-docs/8.2 updated
• Update parent [8.2] Unified publishing — next React increments #4531 Agent progress when the PR opens

H2 QA: perc-devctl qa-up → qa-health → TEST_CMS_URL → npm run test:surface → qa-down.

Leave unassigned. Do not add In Progress.

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