feat(booth): add The Booth — ephemeral media drop board for CC sessions

A standing user-level web server (nh3-dev :8090) that renders drop-folders
under ~/booth-data as ephemeral media "booths" so Claude Code sessions can
surface A/B renders and smoke results to the operator, then let them self-wipe.

- Scan-and-serve model, no database, no upload API — a booth is just a folder.
  A folder's own index.html is served verbatim; otherwise an auto-gallery of
  images / webm+mp4 video / audio is rendered, with <file>.txt caption sidecars
  folded in (labels A/B pairs).
- 24h TTL from newest mtime in the tree; background sweeper wipes stale booths.
- Path-traversal + symlink-escape guarded; delete via UI button or DELETE API.
- FastAPI + Jinja2, runs from the checkout under systemctl --user (booth.service),
  alongside the other nh3-dev fleet sidecars. 15 tests, all green.
- Homepage tile added (Apps -> The Booth, siteMonitor /healthz).
- Harden the homepage rsync doc: exclude *.bak* and logs/ so --delete can't
  wipe the host's dated services.yaml backups (footgun found deploying this).

booth.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=The Booth — ephemeral media drop board (scan+serve ~/booth-data, 24h TTL)
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+WorkingDirectory=/home/lkraven/development/eshpfi-management/services/booth
+ExecStart=/home/lkraven/development/eshpfi-management/services/booth/.venv/bin/uvicorn booth.app:app --host 0.0.0.0 --port 8090
+Environment=BOOTH_DATA_DIR=/home/lkraven/booth-data
+Environment=BOOTH_TTL_HOURS=24
+Environment=BOOTH_HOST_LABEL=nh3-dev 10.100.10.50
+Environment=BOOTH_SWEEP_INTERVAL_MIN=15
+Restart=on-failure
+RestartSec=3
+
+# User-level unit: install to ~/.config/systemd/user/booth.service and
+#   systemctl --user daemon-reload && systemctl --user enable --now booth.service
+# (loginctl enable-linger lkraven  — so it survives logout, already set on nh3-dev)
+[Install]
+WantedBy=default.target