Add --kms-key-arn flag to add memory (parity with harness/import)

[jariy17]

Summary

The memory schema supports a CMK (encryptionKeyArn) and the CLI already wires it through add harness --memory-encryption-key-arn and import memory — but the standalone add memory command has no flag, creating a parity gap.

Evidence

• AWS: CreateMemory.encryptionKeyArn.
• CLI: schema field at src/schema/schemas/agentcore-project.ts:278; wired via HarnessPrimitive.ts:667 and import-memory.ts:81, but no flag in MemoryPrimitive.tsx.

Proposal

Add an optional --kms-key-arn <arn> flag (no default) to add memory, mapping to the existing encryptionKeyArn schema field. Use --kms-key-arn (not the harness-scoped --memory-encryption-key-arn) to match add dataset/add evaluator/add policy-engine.