fix(memory): return relations connected to requested nodes in openNodes/searchNodes

[DukeDeSouth]

Summary

Fixes #3137 — open_nodes returns empty relations array despite entity having relations in graph.

Root cause: Both openNodes() and searchNodes() filter relations using && (require BOTH endpoints to be in the result set). This means if you call open_nodes(["A"]) and there's a relation A → B, it gets silently dropped because B isn't in the filtered set.

Fix: Changed the relation filter from && to || — include any relation where at least one endpoint is in the result set. This matches standard graph-query semantics: opening a node should reveal all its edges, not just edges to other opened nodes.

Before (broken)

open_nodes(["2025-12-17"])
→ entities: [2025-12-17], relations: []  // relations silently dropped!

After (fixed)

open_nodes(["2025-12-17"])
→ entities: [2025-12-17], relations: [{from: "2025-12-17", to: "incident/example", ...}]

Changes

• src/memory/index.ts: Changed && → || in relation filtering for both openNodes() and searchNodes()
• src/memory/__tests__/knowledge-graph.test.ts: Updated existing tests and added new cases:
  • Outgoing relations to nodes not in the open set
  • Incoming relations from nodes not in the open set
  • Relations connected to a single opened node (both directions)
  • searchNodes returning outgoing relations to unmatched entities

Test plan

• All 45 existing tests pass (vitest run)
• New tests verify outgoing/incoming relations are returned for single-node queries
• read_graph behavior unchanged (returns all relations)
• Empty node list still returns empty graph
• Non-existent nodes still return empty result

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