Attribute empty expand results to active filters, not exhaustion

[mig-builds]

Closes #2060

What changed

useExpandNode's toast message after an empty expansion result no longer always says "No more neighbors to expand." That message is only accurate when no filters were applied. When the request carried non-empty attributeFilters and the result came back empty, the toast now says "No neighbors matched your filters" instead, since the node may still have neighbors that the filter excluded.

Applied at both call sites (expandNode for a single node, expandNodes for multiple), since the fix path in the issue noted the multi-node path could gain filter support later.

Verification

• Added tests covering both the generic exhausted case and the filtered-empty case, for both expandNode and expandNodes.
• pnpm checks (lint, format, types) passes.
• pnpm test passes except for one pre-existing, unrelated failure in safeSessionStorage.test.ts (confirmed it fails identically on main without this change).