fix(deploy): report what enable actually did, and arm the tier's timers

Two lies in the unit loop, both reported as success:

- `systemctl --user enable live-sync.service` fails on every deploy — the file has
  no [Install] section, because live-sync.timer is what arms it. The result was
  swallowed by `|| true` and the tool printed ENABLE anyway, so the line an
  operator reads after a rebuild was false on every box, on the repo's own
  heartbeat. The [Install] section is readable from the file being deployed, so
  the tool now checks it and prints INERT with the reason instead of making a
  call that cannot succeed; a real enable failure prints INERT too.
- The loop walked *.service only. live-sync.timer was never enabled by anything,
  so a rebuilt box got the heartbeat and no schedule for it. Timers are walked
  now; a timer has no ExecStart, so the "does this unit belong on this box" test
  runs against the service it activates.

The systemctl stub models systemd's refusal (no [Install] section -> non-zero),
which is what makes the new tests red against the old loop; both new tests were
run red first, and the five existing unit tests still pin #44's semantics.

Refs #60

tests/deploy.bats

@@ -37,7 +37,22 @@ if [ "$2" = is-enabled ]; then
   printf '%s\n' "$state"
   case "$state" in disabled | "") exit 1 ;; *) exit 0 ;; esac
 fi
-exit 0
+if [ "$2" = enable ]; then
+  # Modelled, not stubbed flat: systemd refuses to enable a unit whose file has no [Install]
+  # section, and the deployed file is what it reads. A stub that always says yes hides the
+  # one case this repo actually ships (live-sync.service is driven by its timer).
+  target=""
+  for a in "$@"; do
+    case "$a" in
+      *.service | *.timer | *.socket) target="$a" ;;
+    esac
+  done
+  file="$HOME/.config/systemd/user/${target##*/}"
+  if [ -e "$file" ] && ! grep -q '^\[Install\]' "$file"; then
+    printf 'The unit files have no installation config (WantedBy=, RequiredBy=, Also= settings in the [Install] section). This means they are not meant to be enabled using this command.\n' >&2
+    exit 1
+  fi
+fi
 STUB
   chmod +x "$TEST_TMP/bin/systemctl"
   export PATH="$TEST_TMP/bin:$PATH"
@@ -57,6 +72,21 @@ systemd_unit() {
     > "$REPO/dotfiles/systemd-user/.config/systemd/user/$1"
 }
 
+# systemd_unit_no_install <name> <ExecStart> — a unit nothing can enable (live-sync.service:
+# it is pulled in by live-sync.timer, so it carries no [Install] section on purpose).
+systemd_unit_no_install() {
+  mkdir -p "$REPO/dotfiles/systemd-user/.config/systemd/user"
+  printf '[Unit]\nDescription=%s\n[Service]\nType=oneshot\nExecStart=%s\n' "$1" "$2" \
+    > "$REPO/dotfiles/systemd-user/.config/systemd/user/$1"
+}
+
+# systemd_timer <name> <service-name> — a schedule; it has no ExecStart of its own.
+systemd_timer() {
+  mkdir -p "$REPO/dotfiles/systemd-user/.config/systemd/user"
+  printf '[Unit]\nDescription=%s\n[Timer]\nOnCalendar=hourly\nPersistent=true\n[Install]\nWantedBy=timers.target\n' "$1" \
+    > "$REPO/dotfiles/systemd-user/.config/systemd/user/$1"
+}
+
 @test "generated theme output is never adopted into a symlink" {
   repo_file "ghostty/.config/ghostty/themes/noctalia" 'background = "#f43841"'
   live_file "$HOME/.config/ghostty/themes/noctalia" 'background = "#f43841"'
@@ -152,3 +182,31 @@ systemd_unit() {
   grep -q 'systemctl --user enable heartbeat.service' "$STUB_LOG"
   ! grep -q -- '--now' "$STUB_LOG"
 }
+
+@test "a unit nothing can enable is reported as what it is, never as ENABLE" {
+  # `systemctl --user enable live-sync.service` fails on every deploy: the file has no
+  # [Install] section (its timer arms it), and systemd says so with a non-zero exit. The
+  # deploy swallowed that and printed ENABLE, so the one line the operator reads to learn
+  # what a rebuild armed was false on every box, on the repo's own heartbeat.
+  systemd_unit_no_install heartbeat.service /bin/sh
+  printf 'linked\n' > "$UNIT_STATE"
+  run "$REPO/scripts/deploy.sh"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"heartbeat.service"*"[Install]"* ]]
+  [[ "$output" != *"ENABLE heartbeat.service"* ]]
+  # No futile call: the section is readable from the file being deployed.
+  ! grep -q 'systemctl --user enable heartbeat.service' "$STUB_LOG"
+}
+
+@test "a timer in the tier is armed, because a service on its own has no schedule" {
+  # The loop walked *.service only. On a rebuilt box live-sync.service is deployed and the
+  # timer is never enabled, so the heartbeat that commits machine state simply does not run
+  # — and the deploy report says nothing about it.
+  systemd_unit heartbeat.service /bin/sh
+  systemd_timer heartbeat.timer heartbeat.service
+  printf 'disabled\n' > "$UNIT_STATE"
+  run "$REPO/scripts/deploy.sh"
+  [ "$status" -eq 0 ]
+  [[ "$output" != *"SKIP   heartbeat.timer"* ]]
+  grep -q 'systemctl --user enable --now heartbeat.timer' "$STUB_LOG"
+}