v0.9.0: Storage paths registry, per-app HDD_PATH resolution, storage management UI

- Fix backup toggles not appearing (read each app's own HDD_PATH from app.yaml)
- Storage paths registry in settings.json with auto-discovery from deployed apps
- Settings page "Adattárolók" section with disk usage, add/remove/default/schedulable
- Deploy page path field as dropdown of registered storage paths
- Health check storage monitoring (mount point, disk usage alerts)
- Mount-point validation utilities (Linux syscall + cross-platform stubs)
- Controller docker-compose mount changed to /mnt:/mnt:rw for multi-storage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/web/templates/style.css

@@ -1976,6 +1976,85 @@ a.stat-card:hover {
     border-color: rgba(218, 54, 51, 0.3);
 }
 
+/* --- Settings page: Storage paths --- */
+.storage-paths-list {
+    display: flex;
+    flex-direction: column;
+    gap: .75rem;
+}
+.storage-path-item {
+    background: var(--bg-secondary);
+    border: 1px solid var(--border-color);
+    border-radius: 8px;
+    padding: 1rem;
+}
+.storage-path-header {
+    display: flex;
+    justify-content: space-between;
+    align-items: flex-start;
+    gap: 1rem;
+    margin-bottom: .5rem;
+}
+.storage-path-info {
+    display: flex;
+    flex-direction: column;
+    gap: .15rem;
+}
+.storage-path-label {
+    font-weight: 600;
+    font-size: .95rem;
+}
+.storage-path-path {
+    font-family: 'JetBrains Mono', monospace;
+    font-size: .8rem;
+    color: var(--text-muted);
+}
+.storage-path-badges {
+    display: flex;
+    gap: .35rem;
+    flex-shrink: 0;
+    flex-wrap: wrap;
+}
+.storage-path-details {
+    margin: .5rem 0;
+}
+.storage-path-disk {
+    margin-bottom: .5rem;
+}
+.storage-path-meta {
+    font-size: .8rem;
+    color: var(--text-muted);
+}
+.storage-path-actions {
+    display: flex;
+    gap: .5rem;
+    margin-top: .75rem;
+    flex-wrap: wrap;
+}
+.btn-xs {
+    padding: .2rem .5rem;
+    font-size: .75rem;
+    border-radius: 6px;
+}
+.btn-danger-outline {
+    background: transparent;
+    border: 1px solid rgba(218, 54, 51, 0.5);
+    color: var(--red);
+}
+.btn-danger-outline:hover {
+    background: var(--red-bg);
+    border-color: var(--red);
+}
+.storage-add-details {
+    margin-top: .5rem;
+}
+.storage-add-details[open] summary {
+    margin-bottom: 1rem;
+}
+.storage-add-form {
+    margin-top: .75rem;
+}
+
 /* Responsive */
 @media(max-width: 768px) {
     .sidebar { width: 100%; height: auto; position: relative; border-right: none; border-bottom: 1px solid var(--border-color); }