Migrate 25 route files to throw-based error handling

Converted routes:
- All auth routes (totp.js, keys.js, sso-gate.js)
- Recipe deployment routes (deploy.js, manage.js, index.js)
- App deployment routes
- Config routes (assets, backup, settings)
- ARR routes (config, credentials)
- Infrastructure routes (dns, services, sites, logs)
- Additional routes (browse, ca, health, license, notifications, tailscale, updates)

Changes:
- Replaced ctx.errorResponse() with throw statements
- Replaced errorResponse() with throw statements
- Added proper error imports to each file
- 400 errors → ValidationError
- 401 errors → AuthenticationError
- 403 errors → ForbiddenError
- 404 errors → NotFoundError
- 409 errors → ConflictError
- 500 errors → Handled by middleware

Result: 25 files migrated, ~150 error responses standardized

dashcaddy-api/routes/config/settings.js

@@ -1,6 +1,7 @@
 const fsp = require('fs').promises;
 const { validateConfig } = require('../../config-schema');
 const { exists } = require('../../fs-helpers');
+const { ValidationError } = require('../errors');
 
 module.exports = function(ctx) {
   const express = require('express');
@@ -22,7 +23,7 @@ module.exports = function(ctx) {
     const incoming = req.body;
 
     if (!incoming || typeof incoming !== 'object') {
-      return ctx.errorResponse(res, 400, 'Invalid config object');
+      throw new ValidationError('Invalid config object');
     }
 
     // Merge with existing config so partial saves don't wipe fields