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

docs/web-ui/shape.md

@@ -19,7 +19,7 @@
   from `@hive/shared` (was `hive-fr0nt`); the dashboard ships one
   CSS bundle per page (`colors.css` + `theme.css` + `common.css`,
   loaded by every page, plus a page-specific bundle —
-  `dashboard.css` / `flow.css` / `logs.css` / `home.css` /
+  `dashboard.css` / `flow.css` / `home.css` /
   `stats.css` / `core.css` / `builds.css`);
   `common.css` inlines `@hive/shared`'s
   `base.css` + `terminal.css` + `tabs.css` + `chrome.css` +
@@ -247,7 +247,7 @@ values rather than per-row caches.
 tagged with `data-restore-key="<stable-key>"` survives the
 refresh. `snapshotOpenDetails()` walks managed sections before
 render, `restoreOpenDetails()` re-applies after. Long-content
-drill-ins (file previews, diffs, journald logs) now open in the
+drill-ins (file previews, diffs) now open in the
 **side panel** (see below) rather than expanding inline. The
 dashboard's own answered-questions history list was the only
 `<details data-restore-key>` consumer and is gone
@@ -261,8 +261,8 @@ that needs it rather than ripped out along with their one caller.
 swipes in from the right — a singleton `#side-panel` with a
 titled header, a close button, and a scrollable body. Closes on
 the button, selecting the backdrop, or `Escape`. `Panel.open(title,
-node)` swaps the body; the JS builders for file previews and
-journald logs all render into it. **The
+node)` swaps the body; the JS builder for file previews
+renders into it. **The
 drawer width is drag-to-resize**: a thin 6px hit-strip on
 the left edge captures pointer events, resizes the drawer in
 real-time (pointer capture keeps dragging even if the cursor