DC-101: Disk Space Monitor + Product Vision

Backend:
- src/monitoring/disk-space-monitor.js: monitors Docker disk usage against
  user-configured budget, auto-cleans at thresholds, breaks down by category
- routes/disk-space.js: GET /disk, GET /disk/breakdown, POST /disk/config,
  POST /disk/cleanup endpoints
- src/app.js: wire DiskSpaceMonitor into startup, 10-min check interval
- All 1539 tests pass

Product Vision (PRODUCT-VISION.md):
- DashCaddy is a self-hosting platform, not just a dashboard
- Core value: 'Self-host anything in 30 seconds'
- Three pillars: One-click deploy, zero-config networking, self-healing infra
- vs Portainer/CasaOS/Yunohost positioning

New backlog tasks (P5 tier, DC-101–108):
- Disk budget, one-click deploy with auto Caddyfile+DNS, container
  auto-discovery, app catalog, smart wizard, visual Caddy builder,
  disaster recovery, multi-host fleet management

47 total backlog tasks, ~110 hr of work, cron running every 2h.

scripts/docker-space-cleanup.sh

@@ -0,0 +1,65 @@
+#!/bin/bash
+# DashCaddy Docker Space Management
+# Runs via cron to keep Docker disk usage under control
+# Prevents the overlay2 + dangling volumes + stale images that fill the disk
+
+set -euo pipefail
+
+MAX_DISK_PCT=85  # Alert if disk usage exceeds this
+LOG_PREFIX="[dc-disk]"
+
+# 1. Remove dangling (untagged) images
+echo "$LOG_PREFIX Pruning dangling images..."
+docker image prune -f --filter "dangling=true" 2>/dev/null || true
+
+# 2. Remove unused volumes (volumes not attached to any container)
+echo "$LOG_PREFIX Pruning unused volumes..."
+docker volume prune -f 2>/dev/null || true
+
+# 3. Remove old build cache
+echo "$LOG_PREFIX Pruning build cache..."
+docker builder prune -f --keep-storage 500m 2>/dev/null || true
+
+# 4. Remove stopped containers older than 7 days
+echo "$LOG_PREFIX Pruning old stopped containers..."
+docker container prune -f --filter "until=168h" 2>/dev/null || true
+
+# 5. Remove images not used by any container (keep only running images)
+# Only remove images older than 7 days to avoid breaking recent updates
+echo "$LOG_PREFIX Pruning unused images (>7 days old)..."
+docker image prune -a -f --filter "until=168h" --filter "dangling=false" 2>/dev/null || true
+
+# 6. Truncate container log files that are bigger than 100MB
+echo "$LOG_PREFIX Checking container logs..."
+for logfile in /var/lib/docker/containers/*/*-json.log; do
+  if [ -f "$logfile" ]; then
+    size=$(stat -c%s "$logfile" 2>/dev/null || echo 0)
+    if [ "$size" -gt 104857600 ]; then  # 100MB
+      echo "$LOG_PREFIX Truncating $(basename $logfile) ($(( size / 1048576 ))MB)"
+      truncate -s 0 "$logfile"
+    fi
+  fi
+done
+
+# 7. Vacuum journald logs to 200MB
+echo "$LOG_PREFIX Vacuuming journal logs..."
+journalctl --vacuum-size=200M 2>/dev/null || true
+
+# 8. Clear pip/npm caches that grow over time
+echo "$LOG_PREFIX Clearing stale caches..."
+rm -rf /root/.cache/pip/cache/html 2>/dev/null || true
+rm -rf /root/.cache/npm/_cacache 2>/dev/null || true
+
+# 9. Report disk usage
+USAGE=$(df / | tail -1 | awk '{print $5}' | tr -d '%')
+FREE_GB=$(df -h / | tail -1 | awk '{print $4}')
+echo "$LOG_PREFIX Disk usage: ${USAGE}% (${FREE_GB} free)"
+
+if [ "$USAGE" -gt "$MAX_DISK_PCT" ]; then
+  echo "$LOG_PREFIX WARNING: Disk usage above ${MAX_DISK_PCT}%!"
+  # More aggressive: remove ALL images not used by running containers
+  echo "$LOG_PREFIX Aggressive prune: removing all unused images..."
+  docker image prune -a -f 2>/dev/null || true
+fi
+
+echo "$LOG_PREFIX Done."