Restart Resume — Rebuild every session post-reboot

Restore every tmux Claude session captured by /restart-process — recreates the original tmux layout (sessions, windows, panes with correct geometry via window_layout strings) and spawns FRESH claude processes (NOT --resume) with each pane's captured handoff as the first user message. Use when you say '/restart-resume', 'resume sessions after reboot', 'restore my tmux setup', 'bring back my claudes', 'I just rebooted - restore', or when a SessionStart hook surfaces a pending restart manifest banner. Reads the manifest at `$RESTART_HANDOFFS_DIR/latest/manifest.json` (default `~/.cache/claude-restart/latest/manifest.json`) — verifies checksum + schema before doing anything. …