topology: drop the parent field and the hierarchy it fed

`topology.json` was a map of `name -> parent | null`, and that value fed
the whole agent hierarchy: `<parent>` / `<children>` recipient sentinels,
the reparenting API (CLI verb, wire verb, dashboard endpoints, DAG node),
the dashboard tree, the rebuild depth sort, and an unconditional
bind-mount grant giving every agent RW on its direct children's state.

Per the operator's ruling the field goes, and with it all of the above.
The file survives as what remains once the value is gone: the roster of
agent names, which is the set `ManageRootAgent` grants mounts over. It is
now a JSON array; `read` still accepts the old map shape and keeps its
keys, so a hive that upgrades across this does not blank its roster (and
so no capability holder loses its mounts for the length of that window).

Two sites kept their behaviour under a different recipient rather than
losing it. Both addressed `<parent>`, which the broker already resolved to
`operator` for a root agent, and every agent is now what that fallback
called a root:

- the harness's turn-failure / plugin-failure notification
  (`Surface::send_to_parent` -> `send_to_operator`), and
- the send allow-list's always-permitted escape hatch, so an agent with a
  restrictive allow-list still has a way to say it is stuck.

What is NOT preserved, deliberately: an agent with no capability no longer
sees any other agent's dirs. `ManageRootAgent`'s own grant is unchanged --
still every agent in the roster, still state RW + config RO, still no
`harness`.

The dashboard's reparenting control (the M0V3 picker) is deleted with its
CSS. The tree rendering that reads `ContainerView.parent` is left for the
frontend owner -- it degrades to a flat list with the field gone.

hive-c0re/src/container_view.rs

@@ -49,14 +49,6 @@ pub struct ContainerView {
     /// for this agent's input.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub deployed_sha: Option<String>,
-    /// Name of this agent's parent in the agent hierarchy. `None`
-    /// marks the agent as root-level; the dashboard renders it without
-    /// indentation. Sourced from `meta/topology.json` (single source of
-    /// truth, hive-c0re-owned) — NOT from per-agent agent.nix, because
-    /// an agent shouldn't be able to unilaterally declare its own place
-    /// in the tree. See `docs/agent-lifecycle/agent-hierarchy.md::Where the tree lives`.
-    #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub parent: Option<String>,
     /// The Claude model the agent's harness is currently using, read from
     /// `state/hyperhive-harness.json["active_model"]`. `None` when the
     /// agent has never started a turn or the field is absent. Only
@@ -121,7 +113,6 @@ impl From<ContainerView> for hive_sh4re::container::AgentStatusRow {
             needs_login: v.needs_login,
             deployed_sha: v.deployed_sha,
             pending_reminders: 0,
-            parent: v.parent,
             paused: v.paused,
             active_model: v.active_model,
             status_text: v.status_text,
@@ -164,13 +155,8 @@ fn agent_url_for_domain(domain: &str, name: &str) -> String {
 pub async fn build_all(hive: &crate::coordinator::HiveEnv) -> Vec<ContainerView> {
     let raw = lifecycle::list().await.unwrap_or_default();
     let locked = read_meta_locked_revs();
-    // Pull the topology map once and look up each agent's parent below.
-    // Empty / absent topology.json → every agent root-level (safe
-    // degradation for fresh installs that haven't run sync_agents yet).
-    let topology = crate::topology::read();
-    // Same once-per-scan treatment as the topology map: the override file
-    // is read here and resolved per agent below, rather than re-read for
-    // every container on every SSE scan.
+    // Read once per scan rather than re-read for every container on every
+    // SSE scan.
     let limits = crate::resource_limits::read();
     let mut out = Vec::new();
     for c in &raw {
@@ -189,7 +175,6 @@ pub async fn build_all(hive: &crate::coordinator::HiveEnv) -> Vec<ContainerView>
         let needs_update =
             crate::auto_update::agent_config_pending(logical.as_str(), deployed_full).await;
         let deployed_sha = deployed_full.map(|s| s[..s.len().min(12)].to_owned());
-        let parent = topology.get(logical.as_str()).cloned().flatten();
         // One `systemctl` call for both facts: `unit_state` is the same
         // shell-out `is_running` makes, minus `--quiet`. Asking twice would
         // double the per-agent subprocess count on every SSE scan.
@@ -252,7 +237,6 @@ pub async fn build_all(hive: &crate::coordinator::HiveEnv) -> Vec<ContainerView>
             needs_update,
             needs_login,
             deployed_sha,
-            parent,
             active_model,
             status_text,
             status_set_at,
@@ -547,7 +531,6 @@ mod tests {
             needs_update: true,
             needs_login: false,
             deployed_sha: Some("abc123def456".to_owned()),
-            parent: Some("bob".to_owned()),
             active_model: Some("claude-opus".to_owned()),
             status_text: Some("shipping".to_owned()),
             status_set_at: Some(Utc.timestamp_opt(1_700_000_000, 0).unwrap()),
@@ -563,7 +546,6 @@ mod tests {
         assert!(row.needs_update);
         assert!(!row.needs_login);
         assert_eq!(row.deployed_sha.as_deref(), Some("abc123def456"));
-        assert_eq!(row.parent.as_deref(), Some("bob"));
         assert!(row.paused);
         assert_eq!(row.active_model.as_deref(), Some("claude-opus"));
         assert_eq!(row.status_text.as_deref(), Some("shipping"));