Devnet7 Tests FCR With Safe Block Hash and BLS Tweaks

FCR-Gloas devnet7 testing underway, with client comparison on historical data. Spec updates: PR #5449 adds `safe_execution_block_hash` to FCR tests; #5489 computes real aggregate pubkeys with BLS disabled; #5498 runs FCR at epoch boundary; #5499 fixes duplicate FCR run. Fuzzing covers client implementations. Meeting Tuesday, August 4, 2026, 12:00 UTC.