cli: switch to clap, add notify-timeout, improve status display

Replace manual arg parsing with clap derive for the full command set.
Single source of truth for command names, args, and help text.

Add notify_timeout (default 2min) — controls how long after last
response before notifications inject via tmux instead of waiting
for the hook. Separate from idle_timeout (5min) which controls
autonomous prompts.

Improve `poc-daemon status` to show both timers with elapsed/configured
and block reason, replacing the terse one-liner.

Add new Status fields over capnp: idleTimeout, notifyTimeout,
sinceActivity, sinceUser, blockReason.

ExecStart in poc-daemon.service now uses `daemon` subcommand.

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

Cargo.toml

@@ -11,6 +11,7 @@ serde_json = "1"
 bincode = "1"
 regex = "1"
 chrono = "0.4"
+clap = { version = "4", features = ["derive"] }
 libc = "0.2"
 faer = "0.24.0"
 rkyv = { version = "0.7", features = ["validation", "std"] }