[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.

start.sh

@@ -167,6 +167,8 @@ docker run -d --restart unless-stopped --name ${CONTAINER_NAME} \
   -v /usr/bin/tailscale:/usr/bin/tailscale:ro \
   -v /var/run/tailscale:/var/run/tailscale:ro \
   -v /etc/ssl/sami-ca:/etc/ssl/sami-ca:ro \
+  -v /var/log/journal:/var/log/journal:ro \
+  -v /usr/bin/journalctl:/usr/bin/journalctl:ro \
   -e NODE_ENV=production \
   -e SERVICES_FILE=/app/data/services.json \
   -e CONFIG_FILE=/app/data/config.json \