feat: allow filtering neighbor expansion by vertex ID

[vishwakt]

Closes #274

Problem

When expanding a node's neighbors, you could only narrow the results by property values. There was no way to target a specific neighbor by its ID, which is what the issue asks for.

Approach

I'd love a sanity check on the approach before polishing further, happy to change any of it.

1. UI (NodeExpandFilters / NodeExpandContent)

• Added "ID" as the first option in the "Filter to narrow results" dropdown.
• ID is offered even for neighbor types that have no searchable attributes, so the filter section now renders whenever a neighbor type is selected (previously it was hidden when a type had no searchable attributes).
• The ID is not a real property, so NodeExpandContent partitions ID filter rows out of the property filterCriteria and into a new filterByIds request field. A reserved sentinel name (ID_FILTER_NAME) marks the ID option; it never reaches the connectors.

2. Request contract (NeighborsRequest)

• Added an optional filterByIds?: Array<VertexId>. This keeps ID filtering fully separate from the property-based filterCriteria path.

3. Connectors each translate filterByIds into their native id filter:

• Gremlin: hasId(...)
• openCypher: ID(tgt) IN [...]
• SPARQL: FILTER(?neighbor IN (...))

Testing

• Added ID-filter cases to the Gremlin, openCypher, and SPARQL oneHop* template tests (single ID, and multiple IDs combined with a type filter).
• pnpm checks and pnpm test pass (2071 tests).

Open questions for maintainers

1. ID filter placement — I put "ID" at the top of the dropdown and default a new filter row to it. Happy to move it to the bottom if you'd rather keep property filters as the default.
2. Always showing the filter section — this is a small behavior change for types with no searchable attributes. It seemed necessary so ID is always filterable, but let me know if you'd prefer to gate it differently.
3. Multiple IDs — multiple ID rows are combined as an IN list (OR). Property filters remain AND-combined. Let me know if you'd expect different semantics.