feat: add listMemories tool to the Supermemory MCP server

[mvanhorn]

Summary

Agents can now enumerate stored memories through a new listMemories tool on the Supermemory MCP server, returning a page of memory records plus a nextCursor for paging rather than only the top-K of a recall query.

Why this matters

Issue #1030 notes the MCP server in apps/mcp/src/server.ts only exposed memory, recall, and listProjects, so there was no way to list memories to audit, bulk-clean, or diff them before a save/forget. The new SupermemoryClient.listMemories in apps/mcp/src/client.ts accepts containerTag, limit, cursor, sort, and a substring filter, normalizing results the same way search() does, and the fourth registerTool block in server.ts mirrors the recall registration with a Zod schema that clamps limit to 1..200 and validates sort, returning { memories, nextCursor } scoped by the existing containerTag semantics.

Testing

The Zod input schema is exercised at registration: out-of-range limit and invalid sort are rejected with validation messages before reaching the API, and the empty-store path returns an empty list with a null cursor. Verified by building the MCP package; full suite runs in CI.

Fixes #1030