Infer edge connections from graph exploration

[kmcginnes]

Description

When users explore the graph and edges are returned from queries, the edge types are correctly added to the schema, but the edge connections (source vertex type → edge type → target vertex type) are not inferred. This means the Schema Explorer diagram does not show new relationships discovered through exploration until the database summary API catches up.

• Add required vertexLookup parameter to updateSchemaFromEntities to infer EdgeConnection entries from edges and their endpoint vertex types
• New VertexTypeLookup interface with createVertexTypeLookup factory that chains existing Map<VertexId, Vertex> instances with O(1) construction (no copying)
• New mergeEdgeConnections function handles multi-label vertices, deduplication, and preserves existing connections (including their count)
• New createEdgeConnection helper for constructing EdgeConnection objects from plain strings
• Update call sites (useAddToGraph, useUpdateSchemaFromEntities, FakeExplorer) to build and pass the vertex lookup from the entity batch + canvas state, with batch vertices taking priority
• Schema refresh continues to overwrite edge connections entirely (current behavior preserved)

Validation

• 7 unit tests for edge connection inference (basic, multi-label, unresolvable endpoints, dedup, count preservation, referential equality)
• 6 tests for createVertexTypeLookup (chaining, priority, isEmpty, unknown IDs)
• 5 integration tests through useAddToGraph and useUpdateSchemaFromEntities verifying end-to-end inference and batch-over-canvas priority
• All 153 test files pass (1678 tests)
• pnpm checks passes (lint, format, types)

Related Issues

• Closes Schema Explorer missing edge connections inferred from graph exploration #1720
• Part of Schema Visualization - Part 2 #1486

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.

[acarbonetto]

Refactor and code looks good. Please fix conflicts.

nit: there's a couple of cases where we could add tests for the empty/null case, but I don't think this is very important.