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/deploy.html

@@ -114,6 +114,22 @@
                            {{if $.AlreadyDeployed}}disabled{{end}}>
                     <span class="toggle-label">Igen</span>
                 </label>
+                {{else if eq .Type "path"}}
+                {{if $.StoragePaths}}
+                <select id="field-{{.EnvVar}}" name="{{.EnvVar}}" class="form-control"
+                        {{if $.AlreadyDeployed}}disabled{{end}}>
+                    {{range $.StoragePaths}}
+                    <option value="{{.Path}}">{{.Label}} ({{.Path}})</option>
+                    {{end}}
+                </select>
+                {{else}}
+                <input type="text" id="field-{{.EnvVar}}" name="{{.EnvVar}}"
+                       class="form-control" value="{{.Default}}"
+                       placeholder="{{.Placeholder}}"
+                       {{if .Required}}required{{end}}
+                       {{if $.AlreadyDeployed}}disabled{{end}}>
+                <span class="form-hint" style="color:var(--yellow)">Nincs regisztrált adattároló — adja meg kézzel az útvonalat</span>
+                {{end}}
                 {{else}}
                 <input type="text" id="field-{{.EnvVar}}" name="{{.EnvVar}}"
                        class="form-control" value="{{.Default}}"