[glm-grade=B] feat(monitoring): host journald log viewer (DC-055)

Adds a dedicated dashboard surface for host journald logs (caddy, docker,
dashcaddy-api, ssh, ...) via a read-only bind-mount of /var/log/journal +
journalctl. Closes queue item #2: the only way to see the recurring
'100.120.159.34:5000 i/o timeout' spam in Caddy's health_checker logs was
SSH into DNS2.

Backend (dashcaddy-api/):
- src/monitoring/journald-reader.js (NEW, ~320 lines) wraps journalctl
  with allow-listed unit names (caddy, docker, dashcaddy-api, ssh,
  systemd-journald, tailscaled, networkd-dispatcher), validates
  since/until/search before argv assembly, and uses spawn() with an argv
  array (no shell). Clamps tail at MAX_TAIL_LINES=5000 and stdout at
  MAX_OUTPUT_BUFFER=2MB; streaming also caps at MAX_STREAM_LINES=5000
  via a closure-scoped counter. Maps ENOENT cleanly to 'journalctl
  unavailable'.
- routes/logs.js (+102 lines): three new routes mounted under the
  existing auth-gated apiRouter: GET /api/v1/logs/journal/units,
  GET /api/v1/logs/journal (bounded tail read), and GET
  /api/v1/logs/journal/stream (SSE). Stream route pre-validates unit
  with assertUnitAllowed BEFORE writing SSE headers so an invalid unit
  returns 400 JSON instead of an open stream with an error frame.
- 41 new tests across 2 files covering allow-list enforcement, shell-meta
  rejection in unit/since/until/search, MAX_OUTPUT_BUFFER cap, ENOENT
  mapping, non-zero exit stderr surfacing, and route-level 400-on-bad-unit.
  Full local suite 1831/1831 (+41 net).

Container plumbing (start.sh):
- Two new bind mounts:
    -v /var/log/journal:/var/log/journal:ro
    -v /usr/bin/journalctl:/usr/bin/journalctl:ro
  Bind-mount chosen over privileged systemd-journal remote to keep the
  container unprivileged and the journal access read-only.

Frontend (status/js/):
- journald.js (NEW, ~285 lines) self-contained modal mirroring the
  existing Container Logs modal. SSE via EventSource, debounced search
  (200ms), overflow hint when stream cap is hit, unit dropdown from a
  fixed allow-list that mirrors the backend. Hooked via the new
  '#view-journald-logs' button in the Tools dropdown (next to Container
  Logs).
- build.js (+4 lines) adds journald.js to the features bundle. Bundle
  rebuild succeeded (features.js 27 files, 466 KB raw / 1229 KB min).
  CSP hash unchanged (no inline script changes).

GLM judge (round 1, 178s, 14 tool calls, cold diff + 8 file reads):
GRADE=B. Shell injection fully defended (all four attacker inputs
rejected before spawn). Route-level allow-list holds (streamEntries not
called for bad unit). SSE cleanup correct. Round-2 fix-first applied
same commit: the round-1 stream's 5000-line cap was dead code (counter
on function object never incremented) moved to closure scope and now
actually fires. Also dropped deprecated req.on('aborted') listener
(Node 18+ fires 'close' for both clean and abort).

Container live HEAD 901df86 [glm-grade=B]; deploy via start.sh atomic
swap. Live verify: status.sami=200, container Up + healthy, the new
bundle and index.html served.

dashcaddy-api/routes/logs.js

@@ -6,6 +6,15 @@ const { exists } = require('../src/utilities/fs-helpers');
 const { paginate, parsePaginationParams } = require('../src/utilities/pagination');
 const { NotFoundError, ValidationError, ForbiddenError } = require('../src/utilities/errors');
 const { ok } = require('../src/utils/responses');
+const journald = require('../src/monitoring/journald-reader');
+
+const journaldAvailable = (() => {
+  try {
+    return fs.existsSync('/var/log/journal') && fs.existsSync('/usr/bin/journalctl');
+  } catch (_) {
+    return false;
+  }
+})();
 
 /**
  * Logs route factory
@@ -218,6 +227,99 @@ module.exports = function({ asyncHandler, ok, docker, logDigest, dockerMaintenan
     ok(res, { result });
   }, 'logs-docker-maintenance'));
 
+  // ===== DC-055: Host journald log viewer =====
+  // Reads from the host's /var/log/journal via bind-mount in start.sh.
+  // Returns 503 if the bind-mount isn't present (dev containers, Windows).
+
+  // Allow-list of units the dashboard can stream. Exposed to the client so
+  // the dropdown stays in sync with the server-side allow-list.
+  router.get('/logs/journal/units', asyncHandler(async (req, res) => {
+    if (!journaldAvailable) {
+      return ok(res, { available: false, units: [] });
+    }
+    const units = await journald.listUnits();
+    ok(res, { available: true, units });
+  }, 'logs-journal-units'));
+
+  // Read a bounded tail of entries for a unit.
+  router.get('/logs/journal', asyncHandler(async (req, res) => {
+    if (!journaldAvailable) {
+      throw new Error('journald not mounted in this container (host /var/log/journal + /usr/bin/journalctl required)');
+    }
+    const entries = await journald.readEntries({
+      unit: req.query.unit,
+      tail: req.query.tail,
+      since: req.query.since,
+      until: req.query.until,
+      search: req.query.search,
+    });
+    ok(res, { entries, count: entries.length });
+  }, 'logs-journal-read'));
+
+  // Stream entries as they arrive (Server-Sent Events).
+  router.get('/logs/journal/stream', asyncHandler(async (req, res) => {
+    if (!journaldAvailable) {
+      res.statusCode = 503;
+      res.setHeader('Content-Type', 'text/event-stream');
+      res.write(`data: ${JSON.stringify({ error: 'journald not mounted in this container' })}\n\n`);
+      res.end();
+      return;
+    }
+
+    // Validate BEFORE writing SSE headers — once headers go out we
+    // can't change statusCode. The reader does the same validation but
+    // we want to short-circuit here so the response status reflects the
+    // right category (400 for validation, 503 for bind-mount missing).
+    try {
+      journald.assertUnitAllowed(req.query.unit);
+      if (req.query.since) journald.parseTimestamp(req.query.since, 'since');
+    } catch (err) {
+      // Pass through the global error middleware so the response status
+      // + shape matches every other validation error in the API.
+      throw err;
+    }
+
+    // SSE headers — same convention as /logs/stream/:id.
+    res.setHeader('Content-Type', 'text/event-stream');
+    res.setHeader('Cache-Control', 'no-cache');
+    res.setHeader('Connection', 'keep-alive');
+    res.setHeader('X-Accel-Buffering', 'no');
+
+    let settled = false;
+    const cleanup = (handle) => {
+      if (settled) return;
+      settled = true;
+      try { handle && handle.kill(); } catch (_) { /* already dead */ }
+      try { res.end(); } catch (_) { /* already closed */ }
+    };
+
+    let handle;
+    try {
+      handle = journald.streamEntries(
+        { unit: req.query.unit, since: req.query.since, search: req.query.search },
+        {
+          onData(entry) {
+            if (settled) return;
+            res.write(`data: ${JSON.stringify(entry)}\n\n`);
+          },
+          onError(err) {
+            if (settled) return;
+            res.write(`data: ${JSON.stringify({ error: err.message || String(err) })}\n\n`);
+            cleanup(handle);
+          },
+        }
+      );
+    } catch (err) {
+      res.write(`data: ${JSON.stringify({ error: (err && err.message) || 'stream failed' })}\n\n`);
+      try { res.end(); } catch (_) { /* ignore */ }
+      return;
+    }
+
+    // Modern Node fires 'close' for both clean disconnects and aborts;
+    // the separate 'aborted' listener is deprecated as of Node 18.
+    req.on('close', () => cleanup(handle));
+  }, 'logs-journal-stream'));
+
   // Get logs from a file path (for native applications)
   router.get('/logs/file', asyncHandler(async (req, res) => {
     const { path: logPath, tail = 100 } = req.query;