fix(remote): add confirmed force restart

[abeljim]

Summary

• distinguish an installed remote binary from the still-running daemon version
• make the non-focusable sidebar confirmation use an explicit second click
• add a confirmed Ctrl-R force restart in the selector that reinstalls, verifies the daemon through its private socket handshake and peer credentials, then terminates its PTYs so bridges reconnect through the new binary
• keep the safe sidebar install path non-destructive and report pending activation honestly

Safety

The selector warning states that force restart closes live remote panes and applications. The command targets only the PID returned by kernel credentials for the verified remote-agent Unix socket; it does not search by process name or trust a pidfile.

Verification

• cargo fmt --all -- --check
• cargo check -p flock
• cargo test -p flock-selector: 129 passed
• cargo test -p flock-sidebar: 308 passed
• cargo test remote_agent: 30 passed
• isolated end-to-end force restart against a temporary daemon and socket under /tmp