issue 4531 slice 67: PublishingShell delete a location scheme #5134

Parent: #4531

Slice goal

In PublishingShell Design, on a context's location-scheme row, confirm and delete one location scheme. The scheme disappears from that context only after DELETE succeeds. Cancel does not call the server. HTTP 400/403/409 do not claim it was deleted. Reuse deleteScheme. Map those statuses in the design error region (the current handler only shows a generic message).

One vertical increment (Design delete + Vitest + surface-filtered Playwright + product-docs). Not scheme save (#4702) and not scheme copy (#5109).

Out of scope

• Deleting a content list (sibling)
• Deleting a publishing context (sibling)
• Deleting an edition (issue 4531 slice 63: PublishingShell delete an edition #5083)
• JSF page removal (issue 1372 slice 3: Delete Runtime deep JSF pages under ui/pubruntime (keep index redirect) #1818/issue 1372 slice 2: Delete Design deep JSF pages under ui/publishing (keep index redirect) #1819) and UAT UAT sign-off for unified Publishing UI (SC-001 / SC-003 / SC-008) #1371

Acceptance criteria

• Confirm deletes one location scheme and the row is gone only after success
• Cancel does not call the server
• HTTP 400/403/409 stay in the error region and do not claim success
• Vitest plus surface-filtered Playwright (npm run test:surface)
• product-docs/8.2 publishing page 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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