fix: delete memory items before vector cleanup

[starboyate]

Summary

• Delete item store rows before vector cleanup so a failed store delete cannot leave active items without vectors.
• Keep vector cleanup best-effort after the authoritative store mutation and invalidate retrieval only after the store-delete path succeeds.
• Add regression coverage for store delete failures, vector cleanup failures, no-vector ids, and operation ordering.

Test Plan

• mvn -pl memind-core -Dtest=DefaultMemoryTest test
• mvn -pl memind-core test
• mvn -pl memind-core spotless:check checkstyle:check
• git diff --check

Notes

• Fixes DefaultMemory.deleteItems orphans store rows when vector deletion succeeds but store deletion fails #101.
• This PR intentionally leaves durable orphan-vector sweeping as follow-up because MemoryVector does not currently expose a portable list/delete-by-filter contract.