is_running collapsed every non-active state into false, so a container that
exhausted its bounded restarts read as plain "down" -- indistinguishable
from one an operator stopped deliberately. Bounding the restarts made that
gap sharper: a slow-failing agent used to grind on visibly, now it can stop
quietly.
Adds UnitState + unit_state() beside is_running rather than widening it.
is_running has ~8 call sites and nearly all are reconcile/power logic asking
"is it up? if not, start it" -- a question with two answers. Only the view
builder needs more, and it gets both facts from one systemctl call, since
is-active prints the state when not passed --quiet.
Surfaces as a flat failed flag on ContainerView and AgentStatusRow, matching
the shape those types already document: independent, orthogonally-observed
facts rather than a state machine. serde(default) keeps it order-independent
with the frontend half.
No behaviour change: nothing acts on the flag, per the ruling.
Closes the #3110 split — lib.rs is now just the crate doc comment and
the pub mod list.
journal.rs's new doc comment fixes a pre-existing bug: the old
JournalPriority doc text in lib.rs was actually half Capability's doc
(a leftover from an earlier reorder that moved the code but not the
comment above it).
