BOLT-990: Align Enphase historical backfill coordinator with SolarEdge

Branch artem-agent/enphase-align-historical-with-solaredge. Worktree ../mono-enphase-align-historical. Spec specs/oem-historical-backfill/enphase-align-with-solaredge.md. Enphase coordinator: compute systemsNotFound on normal path, rename systemsFailedToQueue→systemsFailed, add estimatedJobs log, surface systemsNotFound in operation.end. SolarEdge drive-by: early-exit operation.end logs systemsNotFound as a count (matching normal path). Tests: + normal-path systemsNotFound, + all-resolve invariant. Local: 23 Enphase tests pass, 21 SolarEdge tests pass, lint 0 errors, build clean.