Extract shared DeletePageDialog; fix delete-button styling and Special:Schemas i18n

[alistair3149]

Extracts the page-deletion confirmation shared by Special:Schemas, Special:Layouts, and Special:Mappings into one component, and fixes two bugs found.

What this changes

• New components/common/DeletePageDialog.vue — a self-contained confirmation dialog (CdxDialog + generic delete message + a SummaryAction footer configured destructive + trash icon with a "Reason" field) that performs action=delete and notifies. Replaces three byte-identical dialogs + executeDelete bodies.
• Fix — the confirm button was progressive (blue) + checkmark; now destructive (red) + trash icon. All three pages inherited the wrong styling because the confirm button defaulted to progressive/cdxIconCheck.
• Fix — Special:Schemas delete UI rendered raw message keys. Root cause was ResourceLoader registration, not missing messages: the neowiki-schema-delete-* dialog keys and the neowiki-schema-delete aria-label were absent from the ext.neowiki module's messages list. The refactor replaces the per-entity dialog keys with a single generic neowiki-delete-* set (registered once) and registers the orphaned neowiki-schema-delete.
• Rename EditSummary → SummaryAction (no longer edit-specific) + add optional label/placeholder props so the delete dialog can label the field "Reason".
• i18n — retire the 18 per-entity neowiki-{schema,layout,mapping}-delete-{confirm-*,summary-default,success,error} keys for ~8 generic ones. The confirmation message names the entity type ("The mapping EDM will be deleted") — it avoids exposing that a Schema/Layout/Mapping is stored as a page, and drops "permanently" (untrue for MediaWiki's soft delete). Each page supplies its noun via neowiki-{schema,layout,mapping}-noun. Per-entity row-button aria-labels (neowiki-<entity>-delete) stay, since the trigger button lives on each page.

Commits (ordered for review)

1. Rename EditSummary → SummaryAction (pure rename).
2. Add label/placeholder props to SummaryAction.
3. New DeletePageDialog + generic neowiki-delete-* messages.
4. Migrate the three pages, retire per-entity keys, register neowiki-schema-delete.
5. Review fixes (LayoutsPage delete-wiring test + spec-helper rename).
6. Name the entity type in the confirmation message (drop "page"/"permanently").

Judgment calls

• SummaryAction stays bundled (field + button); no reshape. Splitting the button out to use CdxDialog's native primaryAction/defaultAction was considered but rejected: those props are label-only and cannot carry the trash/checkmark icons these buttons rely on.
• Deletion behaviour is preserved — close-on-confirm, default-reason fallback, success/error notify, refetch on @deleted.
• Per-entity row aria-labels stay ("Delete schema", …) — more informative for screen readers than a generic "Delete", and the button is page-specific.

Known / out of scope

• Error-notification shape (pre-existing). The error instanceof Error ? … : String(error) handler is carried over verbatim; mw.Api().post() rejects with a (code, result) pair, so a real API failure shows a raw code. This predates the PR and affects every create/delete dialog uniformly — left for a separate fix.
• public-api.ts breaking rename. The EditSummary export becomes SummaryAction. No in-repo consumer imports it and NeoWiki is pre-production, but an external extension importing EditSummary would break — heads-up for HW.

Verification

make ts-build, make ts-lint, and the full vitest suite (110 files, 1109 tests) pass. New/updated tests: DeletePageDialog.spec (delete flow + destructive/trash wiring), SummaryAction label/placeholder cases, LayoutsPage.spec (delete wiring), and the Schemas/Mappings page specs.

Manual Browser Check

Verified live on the dev wiki as an admin. To reproduce on each of Special:Schemas, Special:Mappings, Special:Layouts:

1. Open the special page and confirm it renders real text — no raw ⟨neowiki-…⟩ keys (this was broken on Schemas, including the row Delete button's label).
2. Click a row's Delete (trash) button. The confirmation dialog should show:
   • Title "Delete <name>?" and body "The <type> <name> will be deleted." with the name in bold and the type noun matching the page (e.g. "The mapping EDM will be deleted." on Mappings) — no "page", no "permanently".
   • A collapsible "Reason (optional)" field (not "Edit summary").
   • A red (destructive) "Delete" button with a trash icon — not a blue button with a checkmark.
3. (Optional) Expand "Reason", type a reason, confirm — the page is deleted, a success toast shows, and the list refreshes.

Verified end-to-end: Schemas ("The schema Company will be deleted."), Mappings ("The mapping EDM will be deleted."), Layouts ("The layout CompanyOverview will be deleted."). Nothing was actually deleted during verification.

_{AI-authored — Claude Code, Opus 4.8 (1M context). Diff not yet human-reviewed; ts-build/lint + full vitest suite green locally, live-verified end-to-end on the dev wiki (all three pages), plus an adversarial code-review pass (2 findings fixed, 2 noted above).}

[alistair3149]

Manually tested the delete and create flow.
There are no regression and the delete reason appears in the log.