Hygiene: scripts, CI, docs and manifests

- scripts/in-namespace.sh set CARGO_TARGET_DIR to the empty string when
  it was unset, which cargo refuses, and dropped RUSTFLAGS, so the run
  in the namespace rebuilt what kernel-tests.sh had just built. Each is
  passed on only where set.
- The README's list of unsupported features still had route reflection
  and graceful restart, both of which exist; the command-line reference
  lacked SIGUSR1 and exit status 75; the HTTP API reference did not say
  what errors look like.
- The event stream said "missed 0 events" for the best-routes stream,
  which does not count what it missed; it leaves the count out now.
- CI lints bgp-bench with its count-memory feature, which nothing built.
- bgp-bench had two unused dev-dependencies; bgp-integration-tests had
  three dependencies that only its tests and examples use.
- install.sh updates apt before installing; two-routers.sh loses an
  unused variable; small things in the web crate.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/web/static/statusz.html

@@ -495,7 +495,7 @@ from <select id="lookup-peer"><option value="">any peer</option></select>
   function describe(ev) {
     switch (ev.type) {
       case 'session_up': return `<span class="ok">session UP</span> with ${esc(ev.peer.name || ev.peer.peer_addr)} AS${ev.peer.peer_asn} (opened by ${ev.peer.direction === 'outbound' ? 'us' : 'peer'})`;
-      case 'route_refresh_requested': return `${esc(ev.peer.name || ev.peer.peer_addr)} AS${ev.peer.peer_asn} asked for a route refresh; re-sent all originated routes`;
+      case 'route_refresh_requested': return `${esc(ev.peer.name || ev.peer.peer_addr)} AS${ev.peer.peer_asn} asked for a route refresh; re-sent its routes`;
       case 'session_down': return `<span class="bad">session DOWN</span> with ${esc(ev.peer_addr)} AS${ev.peer_asn}`;
       case 'local_announced': { const r = ev.route; return `originating ${esc(r.prefix)}` +
         (r.communities.length ? ` [${names(r.communities)}]` : '') + (r.large_communities.length ? ` [${names(r.large_communities)}]` : '') +
@@ -503,7 +503,7 @@ from <select id="lookup-peer"><option value="">any peer</option></select>
       case 'local_withdrawn': return `<span class="warn">no longer originating</span> ${esc(ev.prefix)}`;
       case 'best_changed': return `best route for ${esc(ev.route.prefix)} is now from AS${ev.route.peer_asn} path [${ev.route.summary.as_path.join(' ')}]`;
       case 'best_withdrawn': return `${esc(ev.prefix)} has <span class="warn">no route</span> any more`;
-      case 'lagged': return `<span class="bad">missed ${ev.missed} events</span> on ${esc(ev.stream)}`;
+      case 'lagged': return `<span class="bad">missed ${ev.missed == null ? '' : ev.missed + ' '}events</span> on ${esc(ev.stream)}`;
       default: return esc(JSON.stringify(ev));
     }
   }