feat: VM disk sandboxing — bounded virtual disk per platform

ARCHITECTURE:
- Windows: dedicated WSL2 distro with fixed VHDX, Docker inside
- macOS: Lima VM with fixed disk, Docker inside
- Linux: sparse ext4 loopback image, Docker data-root inside

NEW FILES:
- vm-provisioner.js: core provisioning engine (create/start/destroy/export)
  - Disk presets: Minimal(10GB), Balanced(30GB), Power(100GB), Custom
  - Sparse images that grow on demand (start at ~0 bytes)
  - Full lifecycle: provision → deploy DashCaddy → destroy (clean removal)
  - Data export before uninstall for users who want to migrate
- vm-ipc.js: Electron IPC handlers connecting wizard to provisioner
  - vm:provision, vm:destroy, vm:get-status, vm:export-data, vm:get-presets
- disk-budget-step.js: wizard UI step with preset cards + custom slider
  - Real-time free space check against selected disk size
  - Plain English description of what each tier handles

UPDATED:
- caddyfile-generator.js: docker-compose now includes disk safety env vars
  (health retention, stats caps, memory limits) as defense-in-depth
  even inside the VM sandbox

GUARANTEE: DashCaddy physically cannot exceed the storage budget.
The OS enforces the limit at the disk/image level, not our code.

dashcaddy-installer/src/main/caddyfile-generator.js

@@ -7,6 +7,10 @@ const { DEFAULT_PORTS } = require('../shared/constants');
  *
  * Generates production-grade configs that match the patterns used by the
  * running DashCaddy deployment (CORS snippets, admin origins, PKI, etc.)
+ *
+ * DISK SAFETY: All generated configs include sensible defaults for storage
+ * limits — health retention, stats caps, and memory limits — so a fresh
+ * install will never silently fill a user's disk.
  */
 class CaddyfileGenerator {
   /**
@@ -279,19 +283,43 @@ class CaddyfileGenerator {
   }
 
   /**
-   * Generate docker-compose.yml for running the API server
+   * Generate docker-compose.yml for running the API server.
+   *
+   * DISK SAFETY: Includes env vars for health retention, stats caps, and
+   * memory limits derived from the disk budget the user selected during
+   * install. These prevent the disk-explosion bugs seen in early versions.
+   *
    * @param {string} installPath - Installation directory
    * @param {Object} options - Configuration options
    * @param {number} options.apiPort - API server port
    * @param {string} options.lanIP - Host LAN IP address
    * @param {string} options.tailscaleIP - Host Tailscale IP address
    * @param {string} options.domainMode - Domain mode (local, public, custom-tld)
+   * @param {Object} [options.disk] - Disk budget settings
+   * @param {number} [options.disk.healthRetentionDays=14] - Health history retention
+   * @param {number} [options.disk.healthMaxEntries=500] - Max health entries per service
+   * @param {number} [options.disk.healthCheckInterval=30000] - Health check interval (ms)
+   * @param {number} [options.disk.statsMaxEntries=2000] - Max container stats entries
+   * @param {number} [options.disk.auditMaxEntries=1000] - Max audit log entries
+   * @param {number} [options.disk.backupLimitGB=10] - Backup storage limit
+   * @param {string} [options.dockerDataPath] - Docker data root override
+   * @param {number} [options.memoryLimitMB=1024] - Container memory limit
    */
   generateDockerCompose(installPath, options = {}) {
     const apiPort = options.apiPort || DEFAULT_PORTS.API;
     const adminPort = DEFAULT_PORTS.CADDY_ADMIN;
     const p = this._p.bind(this);
 
+    // Disk budget settings with safe defaults
+    const disk = options.disk || {};
+    const healthRetentionDays = disk.healthRetentionDays || 14;
+    const healthMaxEntries = disk.healthMaxEntries || 500;
+    const healthCheckInterval = disk.healthCheckInterval || 30000;
+    const statsMaxEntries = disk.statsMaxEntries || 2000;
+    const auditMaxEntries = disk.auditMaxEntries || 1000;
+    const backupLimitGB = disk.backupLimitGB || 10;
+    const memoryLimitMB = options.memoryLimitMB || 1024;
+
     // Core volume mounts
     let volumes = `      - ${p(installPath)}/Caddyfile:/caddyfile:rw
       - ${p(installPath)}/services.json:/app/services.json:rw
@@ -308,12 +336,19 @@ class CaddyfileGenerator {
       volumes += `\n      - ${p(installPath)}/certs/pki/authorities/local:/app/pki:ro`;
     }
 
-    // Environment variables
+    // Environment variables — disk safety baked in
     let envVars = `      - CADDYFILE_PATH=/caddyfile
       - CADDY_ADMIN_URL=http://host.docker.internal:${adminPort}
       - ASSETS_PATH=/app/assets
       - CREDENTIALS_FILE=/app/credentials.json
-      - NODE_ENV=production`;
+      - NODE_ENV=production
+      # --- Disk Safety ---
+      - HEALTH_HISTORY_RETENTION=${healthRetentionDays}
+      - HEALTH_MAX_ENTRIES=${healthMaxEntries}
+      - HEALTH_CHECK_INTERVAL=${healthCheckInterval}
+      - CONTAINER_STATS_MAX_ENTRIES=${statsMaxEntries}
+      - AUDIT_MAX_ENTRIES=${auditMaxEntries}
+      - BACKUP_MAX_STORAGE_BYTES=${backupLimitGB * 1024 * 1024 * 1024}`;
 
     if (options.domainMode === 'custom-tld') {
       envVars += `\n      - CA_CERT_PATH=/app/pki/root.crt`;
@@ -339,6 +374,9 @@ ${envVars}
     extra_hosts:
       - "host.docker.internal:host-gateway"
     restart: unless-stopped
+    # Memory limit prevents OOM during startup when all managers init
+    mem_limit: ${memoryLimitMB}m
+    memswap_limit: ${(memoryLimitMB * 2)}m
 `;
 
     return dockerCompose;