fix: bound logged commands and update README for turn-span

[tsilenzio]

Summary

• Truncate the logged command field to 1 KiB at record time (AN-001). It was the one unbounded hook field, and a line longer than the 8 KiB tail window is unreadable by read_last_line, which made the session invisible to the daemon and released the hold mid-turn, exactly the failure class turn-span was built to remove. Nothing reads command since commit detection was deleted, so the bound only trims what future reactors would see.
• Update the README for the shipped turn-span design (AN-003): the whole-turn hold replaces the commit-timeout paragraph, the 2s tick is described as housekeeping rather than the staleness backstop, seven hooks instead of six, the battery max-hold counts battery time, and status now shows the daemon's last decision.

Test plan

• cargo fmt --check, clippy -D warnings, cargo test (30 tests, including truncation char-boundary cases and a worst-case-escaping line-size guarantee) green locally
• End-to-end: a 20 KB command through the real vigil record path produced a 1188-byte line that parses, command bounded at 1024 bytes plus ellipsis
• CI (macOS check/test/clippy/fmt, conventions)