Tasks: CLI output gap detection

• T001 [FR-001] Reproduce output loss using the real CLI in crates/signaltty-cli/tests/cli.rs and attach_stream.py.
• T002 [FR-001] Reject forward byte gaps before cursor mutation in crates/signaltty-cli/src/attach.rs.
• T003 [FR-002] Verify contiguous, overlapping and legacy offset behavior through existing CLI and unit seams.
• T004 [FR-003] Verify canonical input restoration and document reattach recovery in docs/08-ipc.md.
• T005 [FR-001] [FR-002] [FR-003] Complete independent standards/spec review and full verification before publishing.