feat: implement NIP-09 with hard delete

Implement event deletion (NIP-09) using hard delete approach:
- Kind 5 events trigger deletion but are not stored themselves
- ProcessDeletion hard deletes referenced events (DELETE FROM events)
- Only authors can delete their own events (pubkey verification)
- Support multiple event IDs in single deletion request
- No deletions table needed (simpler schema)
- Added 4 deletion tests covering various scenarios
- All 45 tests passing

1 files changed, 1 insertions, 0 deletions

diff --git a/README.md b/README.md
index 61fa0d4..18bef37 100644
--- a/README.md
+++ b/README.md
@@ -100,6 +100,7 @@ See [proto/nostr/v1/nostr.proto](proto/nostr/v1/nostr.proto) for the full API.
   - **WebSocket** (NIP-01 - standard Nostr protocol)
 - ✅ Subscribe/streaming (real-time event delivery)
 - ✅ Subscription management (filter matching, fan-out)
+- ✅ **NIP-09** - Event deletion (hard delete, authors can delete their own events)
 - ✅ **NIP-11** - Relay info document (GET with `Accept: application/nostr+json`)
 
 **Compatible with:**