build agents only from internal/meta; delete the hive's local meta flake

The hive no longer renders, locks or commits a meta flake. A rebuild's
MetaSync node picks the internal/meta commit and records it with the
hyperhive and config pins it holds; Prebuild, Swap and Create build from it,
and a head that does not pin the agent's current config fails the build
naming the agent. hive-priv's meta_rev is required.

Removed: meta.rs sync/lock/render, the manual-rebuild relock, the boot
sweep's hyperhive bump (MetaLock), the update-meta-inputs form and its
panel, MetaWindow, the hive's hyperhive_rev setting.

Kept: agent_set::refresh holds what sync_agents also did (topology.json, the
gateway's agent-socket map and nginx include), called from spawn, destroy,
rebuild and the migration.

The boot reconcile and the stale-start upgrade compare the agent's marker
with the hyperhive pin of internal/meta; the dashboard's deployed chip reads
the config marker a successful build writes.

hive-agent/src/web_ui/actions.rs

@@ -96,8 +96,8 @@ pub(super) async fn post_new_session(State(state): State<AppState>) -> Response
 #[derive(Deserialize)]
 pub(super) struct MarkTodosDoneForm {
     /// Comma-separated todo ids. Same "one field, JS joins the checked
-    /// boxes" shape as `hive-c0re`'s `meta_inputs::MetaUpdateForm` — axum's
-    /// `Form` extractor doesn't natively decode repeated same-name keys.
+    /// boxes" shape — axum's `Form` extractor doesn't natively decode
+    /// repeated same-name keys.
     ids: String,
 }