issue 4531 slice 93: PublishingShell remove one parameter on a location scheme #5333

Parent: #4531

Slice goal

In Publishing design, an admin removes one parameter from one location scheme. The other parameters stay. The name, generator, description, content type, and template stay as they were. The parameter is gone only after success.

Out of scope

Adding a parameter (slice 90). Changing a parameter value in place. Deleting the scheme (slice 67).

Acceptance criteria

• Confirm removes that one parameter and reload no longer lists it. Other parameters and the scheme identity fields are unchanged. Use the existing location-scheme update. WebUI Publishing design + Vitest + H2 surface Playwright + product-docs/8.2/admin/publishing.md.
• Cancel does not write. Removing the last parameter leaves an empty parameter list and does not delete the scheme. HTTP 400, 403, and 409 leave the previous parameters in place.
• Update parent [8.2] Unified publishing — next React increments #4531 Agent progress section.

Leave unassigned. Do not add In Progress.

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