Restore structured output schemas in memory server when SDK supports JSON Schema outputSchema

[ianliuy]

Context

PR #3966 removes outputSchema and structuredContent from the memory server tools to avoid current SDK serialization crashes when Zod schemas are exposed through tools/list.

That is the safest short-term fix, but it also means the memory server no longer demonstrates structured tool output for these tools.

Follow-up

Once the TypeScript SDK supports plain JSON Schema passthrough and validation for outputSchema, restore structured output for the memory server tools:

• create_entities
• create_relations
• add_observations
• delete_entities
• delete_observations
• delete_relations
• read_graph
• search_nodes
• open_nodes

Suggested validation

• Add a regression test that tools/list serializes cleanly with restored output schemas.
• Add or update tests that tool calls can return structuredContent without _zod serialization or validation errors.

[MukundaKatta]

Worth linking the upstream SDK PR/issue here as the explicit unblocker so this doesn't drift forgotten. In the interim, the JSON Schema for each of the 9 tool outputs could ship as part of the tool description string (or a schema_json annotation) so clients can opt in to validation client-side without waiting for SDK passthrough. Not as good as a real outputSchema but better than nothing for downstream tooling that depends on shape contracts.