DC-059: Joi validation middleware + schemas for destructive routes

[grade=B]

- New src/utilities/validate.js: validateBody(schema) middleware + 9 schemas
  (backupConfigUpdate, backupScheduleCreate, backupRestore, backupRestoreFile,
   appDeploy, appRestore, appRevert, assetUpload, logoUpload)
- Uses Joi's authoritative CIDR validator (rejects malformed IPv6 like ::::/64
  that the previous hex/colon regex would have accepted)
- appDeploy.config uses .unknown(true) for forward-compat with template-specific
  fields (sslType, dnsType, plexClaimToken, etc.) — preserves fields the live
  frontend posts, prevents a behavioural regression
- appRestore uses Joi.any().custom() so the empty-body semantics hold under
  middleware stripUnknown (default) — body with extra keys now rejected
- Wired into 8 destructive routes: backups schedule/restore/config, apps
  deploy/restore/revert, assets upload/logo
- Duplicate legacy POST /backups/schedule handler (line 519) marked LEGACY
  with TODO removal note (Express only matches first registration; this
  handler is unreachable under normal routing)
- Removed redundant manual appId check in /backups/schedule (Joi schema
  enforces it)
- Removed unused 'mime' destructure in /assets/favicon (decodeImageData
  validates MIME internally)
- 41 unit tests covering every exported schema + middleware integration
- 1539/1539 Jest tests pass, zero new ESLint warnings

dashcaddy-api/routes/apps/restore.js

@@ -3,6 +3,7 @@ const path = require('path');
 const fs = require('fs');
 const { DOCKER } = require('../../src/utilities/constants');
 const { ok, validationError, notFound, errorResponse } = require('../../src/utils/responses');
+const { validateBody, schemas: valSchemas } = require('../../src/utilities/validate');
 
 const DEFAULT_BACKUP_DIR = process.env.BACKUP_DIR || path.join(__dirname, '..', 'backups');
 
@@ -36,7 +37,7 @@ module.exports = function({ docker, caddy, servicesStateManager, asyncHandler, e
    * Pulls image, creates container, starts it, recreates Caddy config.
    * Skips if container is already running.
    */
-  router.post('/:appId/restore', asyncHandler(async (req, res) => {
+  router.post('/:appId/restore', validateBody(valSchemas.appRestore), asyncHandler(async (req, res) => {
     const { appId } = req.params;
     const services = await servicesStateManager.read();
     const service = services.find(s => s.id === appId);
@@ -183,9 +184,9 @@ module.exports = function({ docker, caddy, servicesStateManager, asyncHandler, e
   }, 'apps-backup-points'));
 
   // Revert a specific app to a backup file (point-in-time restore)
-  router.post('/:appId/revert/:filename', asyncHandler(async (req, res) => {
+  router.post('/:appId/revert/:filename', validateBody(valSchemas.appRevert), asyncHandler(async (req, res) => {
     const { appId, filename } = req.params;
-    const { encryptionKey, restartContainers } = req.body || {};
+    const { encryptionKey, restartContainers } = req.body;
 
     // Security: prevent path traversal
     if (filename.includes('..') || filename.includes('/') || filename.includes('\\')) {