Fix corrupted events with zero-filled IDs/pubkeys/sigs (v0.47.1)

- Add validation in GetEventIdBySerial to ensure sei value is 32 bytes
- Fix fallback-to-legacy bug: return error instead of attempting legacy
  unmarshal on compact format data when event ID lookup fails
- Add upfront validation in UnmarshalCompactEvent for eventId length
- Prevents events with all-zero IDs from being returned to clients

Files modified:
- pkg/database/serial_cache.go: Validate sei value is exactly 32 bytes
- pkg/database/fetch-events-by-serials.go: Return error for compact format
  when eventId missing instead of falling back to legacy unmarshal
- pkg/database/fetch-event-by-serial.go: Same fix for single event fetch
- pkg/database/compact_event.go: Validate eventId is 32 bytes upfront
- pkg/version/version: Bump to v0.47.1

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/database/serial_cache.go

@@ -251,7 +251,11 @@ func (d *D) GetEventIdBySerial(ser *types.Uint40) (eventId []byte, err error) {
 		}
 
 		return item.Value(func(val []byte) error {
-			eventId = make([]byte, len(val))
+			// Validate that the stored value is exactly 32 bytes
+			if len(val) != 32 {
+				return errors.New("corrupted event ID: expected 32 bytes")
+			}
+			eventId = make([]byte, 32)
 			copy(eventId, val)
 			return nil
 		})