1997fe48bb
Adds the doc-mandated IiosProjectionCursor (ordered high-water-mark + rolling checksum per projection/topic/partition) and a reusable ProjectionCursorService.advance(). The checksum is a deterministic fold over the ordered event stream, so replaying the same events reproduces it — the KG-06 proof that replay reproduces projection outcomes. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>