chore: drop dead code and the stale wireguard-tools dependency [P2]

wireguard-tools was still declared in Depends and in the runtime package list installed by
tools/build.sh --prepare-runtime-env. Since peer discovery moved to docker exec, no code
path invokes a host-side wg, and check_host_tools stopped requiring it. The declaration
was therefore installing a package the harness never calls and misrepresenting the actual
architecture to anyone reading the control file. Removed from both places.

Three items were carrying #[allow(dead_code)], which is a way of silencing the compiler
about a real question rather than answering it:

- SysctlTuningStatus.desired duplicated data that is already in .current - every
  SysctlValue holds both the desired and the current value, so the second Vec was the same
  information cloned on every inspect call and read by nobody;
- SysctlValue.managed was always set to true and never read. Ownership is decided per file
  by the marker, not per key, so the field encoded nothing;
- unix_now() in the reboot scheduler, along with the SystemTime and UNIX_EPOCH imports it
  needed. The module works in chrono NaiveDateTime throughout.

All three are removed rather than annotated. The workspace now builds clean under
-D warnings with no dead_code exceptions anywhere.

cargo test --workspace: 158 + 4 passed. clippy -D warnings clean.

docs/ACCEPTANCE_CHECKLIST.md

@@ -177,6 +177,7 @@
 - [ ] Пакет не устанавливает `/etc/awg2-harness/config.toml` автоматически.
 - [ ] Пакет не включает/не стартует сервис автоматически.
 - [ ] Пакет не имеет `Depends`/`Recommends` на `docker.io`; установка Amnezia/Docker внешняя.
+- [ ] Пакет не имеет `Depends` на `wireguard-tools`: peer state читается внутри контейнера, host-side `wg` не используется.
 - [ ] `apt install ./awg2-harness_<version>_amd64.deb` не устанавливает и не заменяет Docker.
 - [ ] `apt install ./awg2-harness_<version>_amd64.deb` проходит на clean Debian 13 Amnezia host.
 - [ ] После ручной установки config `awg2-harness validate-config` проходит.