dashboard: remove the L0GS page and its journal backend

Logs live at swarm level now (VictoriaLogs, read through Grafana
Explore). The hive dashboard's own journal viewer goes, with
everything that existed only to serve it:

- frontend: /logs.html, logs.js, logs.css, the H0M3 "Logs" tile and
  the per-agent menu's "journal logs ->" link. The build-log list
  rules BU1LDS used from logs.css move into builds.css.
- hive-c0re: GET /api/journal/{name} and GET /api/journal-host, and
  priv_client::read_container_journal.
- hive-priv / hive-priv-sock: the ReadContainerJournal request, its
  JournalQuery/JournalOutput wire types and the journalctl -M executor.
- nix: hive-c0re's systemd-journal supplementary group, whose only
  reader was the journal-host handler.
- docs: the L0GS section, the API entry and the security table row.

Closes #5113
Closes #3819

frontend/packages/dashboard/src/builds.css

@@ -1,14 +1,11 @@
 /* ─── /builds.html — BU1LDS page ────────────────────────────────────
    The build lifecycle hub: rebuild queue + live log, meta inputs, and
-   build log history on one page. Carved out of /core.html (rebuild
-   queue + meta inputs) and /logs.html (BUILD tab).
+   build log history on one page.
 
    Imports system-sections.css for rebuild queue + meta inputs + live-log
-   component styles, and logs.css for the build-logs-* component styles.
-   Body-scoped `.logs-shell` rules in logs.css don't apply here
-   (`.builds-shell` body); only the build-logs-* component rules are used. */
+   component styles; the build-logs-* rules for the BUILD L0GS list are
+   below. */
 @import "./system-sections.css";
-@import "./logs.css";
 @import "@hive/shared/jobq-graph.css";
 
 body.builds-shell {
@@ -27,3 +24,116 @@ body.builds-shell {
 .builds-pane[hidden] {
   display: none;
 }
+
+.logs-toolbar {
+  display: flex;
+  gap: 0.6em;
+  align-items: center;
+  margin-bottom: 0.9em;
+  flex-wrap: wrap;
+}
+
+/* ─── build-log list ──────────────────────────────────────────────
+   Scrollable list of log header rows; clicking a row expands full
+   stdout+stderr inline. */
+.build-logs-list {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  overflow-y: auto;
+  flex: 1 1 0;
+  min-height: 0;
+}
+.build-logs-item {
+  border-bottom: 1px solid var(--border);
+  padding: 0.15em 0;
+}
+.build-logs-row-btn {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.4em;
+  align-items: baseline;
+  width: 100%;
+  background: none;
+  border: none;
+  color: var(--fg);
+  font-family: inherit;
+  font-size: 0.85em;
+  text-align: left;
+  padding: 0.25em 0.4em;
+  cursor: pointer;
+  border-radius: 3px;
+}
+.build-logs-row-btn:hover {
+  background: var(--bg-elev);
+}
+.build-logs-kind {
+  font-weight: 600;
+}
+.build-logs-age {
+  font-size: 0.88em;
+}
+.build-logs-cmdline {
+  color: var(--muted);
+  font-size: 0.82em;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  max-width: 40em;
+}
+.build-logs-detail {
+  padding: 0 0.4em 0.4em;
+}
+.build-logs-output {
+  margin: 0.3em 0 0;
+  padding: 0.4em 0.6em;
+  background: var(--crust);
+  color: var(--fg);
+  border: 1px solid var(--purple-dim);
+  font-size: 0.82em;
+  line-height: 1.4;
+  white-space: pre-wrap;
+  word-break: break-word;
+  overflow-x: auto;
+  max-height: 30em;
+  overflow-y: auto;
+}
+.build-logs-dl {
+  color: var(--muted);
+  font-size: 0.8em;
+  text-decoration: none;
+  border: 1px solid var(--purple-dim);
+  padding: 0.1em 0.4em;
+  border-radius: 2px;
+  margin-top: 0.3em;
+  display: none;
+}
+.build-logs-dl:not([hidden]) {
+  display: inline-block;
+}
+.build-logs-dl:hover {
+  color: var(--fg);
+  border-color: var(--purple-dim);
+}
+
+.build-logs-live-badge {
+  margin-bottom: 0.4em;
+}
+
+@keyframes live-pulse {
+  0%,
+  100% {
+    opacity: 1;
+  }
+  50% {
+    opacity: 0.45;
+  }
+}
+.build-logs-live-badge.badge-running {
+  animation: live-pulse 1.4s ease-in-out infinite;
+}
+
+.build-logs-runtime {
+  font-size: 0.85em;
+  color: var(--muted);
+}