swarm: add a declared "paused" agent wanted state

mara (#4170): swarm-ui's wanted-state dropdown could only ever declare
up/offline/destroy, with no way to swarm-declare the existing hive-local
turn-loop pause (`hivectl agent pause|resume`).

`AgentState::Paused` is not a fifth peer of Up/Offline/Destroyed on the
power axis this enum otherwise answers — it's Up plus an orthogonal
turn-loop pause. `hive-c0re`'s `workers::wanted` reconcile loop now
decides the two axes independently (`decide` for power, the new
`decide_pause` for the marker), so a stopped agent declared Paused
converges with both a Start and a Pause in the same pass.

Known, deliberate limitation: a Paused declaration on an agent this
hive has never deployed only reaches Deploy this pass — writing the
pause marker into a harness dir that may not exist yet was judged not
worth the risk, so it converges on the next pass once the agent is
present instead.

swarm-ui's WantedMenu gains a fourth "paused" option (warning-tone
badge). No separate "resume" entry — selecting "up" from a paused row
already clears the marker via the same decide_pause path.

Pause/resume marker writes go through one shared
Coordinator::set_paused_by_name helper, used by both the interactive
dashboard pause/resume handlers and this reconcile loop, instead of
each duplicating the parse-name/write-marker/track-rescan shape.
swarm-ui's "offline" and "paused" confirm dialogs share one
confirmTarget state and one ConfirmDialog instead of two near-identical
copies.

Closes #4170

swarm-controller/src/wanted.rs

@@ -269,7 +269,7 @@ mod tests {
     #[test]
     fn moving_a_destroyed_agent_to_any_other_state_is_refused() {
         let current = br#"{"agents":{"atlas":{"state":"destroyed"}}}"#;
-        for state in [AgentState::Up, AgentState::Offline] {
+        for state in [AgentState::Up, AgentState::Offline, AgentState::Paused] {
             let err = apply(Some(current), "atlas", state).unwrap_err();
             assert!(
                 err.downcast_ref::<super::TerminalStateError>().is_some(),