Agent Skills: event-store-semantics

The authoritative behavioral contract of Quartz's event stores — `IEventStore` and its reference SQLite implementation (`nip01Core/store/sqlite/`). Use when implementing or asserting parity with a Quartz event store (external engines like Vespa, the filesystem store, geode), answering filter-semantics questions (since/until inclusivity, tag OR/AND, multi-filter limits, ordering tiebreaks), or working on the write-path rules for replaceable/addressable supersession, NIP-09 deletions, NIP-40 expiration, NIP-62 vanish, NIP-45 counts, or NIP-50 search inside the store. Every behavior has a named rule id (STORE-Fxx/Wxx/Dxx/Sxx/Cxx) so downstream implementations can annotate divergences precisely.