Add bulk delete by entry type to the Brain UI

[selfcontained]

The Brain explorer could delete one entry at a time, clear a collection, or clear a project — but not "clear just the events", which is what you want when one noisy job floods the event log and the objects and lists around it are still worth keeping.

Each section header (Objects / Lists / Events) now clears that type in the current scope: the selected collection, or every collection in the project when the All pill is active.

Server

• deleteEntriesOfType(repoRoot, type, scope) deletes one entry type in one scope. Lists take their items with them via the existing brain_list_items foreign key cascade.
• deleteFromEntryTable is now the only author of a bulk WHERE clause, the table lookup, and the blank-collection rule. deleteCollection and deleteProject route through it too, so the three paths cannot disagree about scoping.
• toEntryTypeDeleteScope owns "collection XOR allCollections", called by both the route and the store so untyped callers hit the same gate. A missing collection is rejected rather than read as "everything" — the same reason brain_delete_events requires one (Add brain_delete_events MCP tool #928).
• DELETE /api/v1/brain/{objects,lists,events} keeps only HTTP-shaped rules: rejecting array-valued query keys, requiring repoRoot, coercing allCollections. mapBrainValidation turns store rejections into 400s, which the pre-existing collections DELETE now shares.

Web

• The confirmation quotes the scope's real totals, not the rows on screen. The lists are capped at 100 and narrowed client-side by the filter box, so the badge can read 0 / 6 while the dialog offers to delete all six. Totals are read live, so an agent writing entries while the dialog is open moves the number rather than leaving it stale.
• A filter that hides every row of a type keeps the section mounted — otherwise the one control that reaches the hidden rows disappears exactly when it is needed.
• Bulk delete is not offered until totals load, rather than guessing a count and then silently skipping the empty-collection redirect.
• CollapsibleSection stays a layout primitive: one headerAction slot, and visibleCount/totalCount instead of a count whose meaning changed.

Reviews

Three persona reviews ran on this branch; all 10 items are resolved. They caught a filter-to-zero bug that hid the delete-all button, a stale-count snapshot that SSE invalidation made live rather than theoretical, a blank-collection divergence between the two delete paths, and a 500 introduced while fixing that last one.

Testing

• pnpm run check, pnpm run finalize:web
• Vitest: 150 + 56 + 9 test files pass, including 14 new brain store/route tests covering scoped and project-wide deletes, cascade, cross-repo isolation, and every malformed selector returning 4xx. brain-routes.test.ts drives the real Fastify app against a real Postgres via app.inject, so the new endpoints are covered end to end without a browser.
• Playwright: 178 pass. No e2e was added for this feature — the backend is covered by the route tests above, and the frontend wiring is in an area that changes rarely and was verified by hand. The one e2e edit is an exact: true locator fix, needed because getByRole matches accessible names by substring and the new "Delete all ..." buttons otherwise collide with the "All" collection pill.

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