swarm-ui: add agent start/stop, backed by the wanted-state route

hyperhive#3896. The backend for start/stop (Up/Offline wanted-state
declarations) already existed and was merged (#3905's writer, the
PUT /api/hives/{hive}/agents/{agent}/state route) — nothing here was
waiting on Paused/Destroyed, which I'd mistakenly conflated with this
issue in an earlier comment (that's #3803, a different feature).

swarm-controller: merges each row's declared wanted state into
GET /api/agents/status, same shape as the config_pr merge (one read
per distinct hive, not per agent, since a declaration is a hive's
whole agent map).

swarm-ui: AgentsPage gets a "wanted" column — clicking the current-
state badge toggles it (Badge's own chip-plus-control shape, same as
its own header comment's pause/resume example), backed by the PUT
route above. A row with no declaration yet reads its implied current
state off the agent's own last-reported running flag. Stop asks for
confirmation (native window.confirm — no confirm-dialog component
exists in swarm-ui yet); start doesn't.

swarm-controller/src/agent_status.rs

@@ -56,6 +56,15 @@ pub struct AgentStatusRow {
     /// here, is what makes this the single call swarm-ui's agent roster
     /// page needs.
     pub config_pr: Option<crate::forge::ConfigPrStatus>,
+    /// The agent's declared wanted state (`"up"`/`"offline"`), if this
+    /// hive has one on record. Same rule as `config_pr`: always `None`
+    /// out of this reader, filled in by the `GET /api/agents/status`
+    /// handler from `AppState::wanted` — this module has no notion of a
+    /// *declaration* (a swarm-level intent), only of what an agent last
+    /// *reported about itself*, and merging a second bucket's read in
+    /// here would blur that boundary for the same reason `config_pr`
+    /// doesn't merge forge state in directly.
+    pub wanted: Option<String>,
 }
 
 /// A snapshot as retained by the bucket, with the hive it was published
@@ -176,6 +185,7 @@ fn render(
                 age_seconds: None,
                 snapshot: None,
                 config_pr: None,
+                wanted: None,
             },
         })
         .collect();
@@ -219,6 +229,7 @@ fn row(
         age_seconds: age.map(|age| age.as_secs()),
         snapshot: offered.payload.clone(),
         config_pr: None,
+        wanted: None,
     }
 }