[grade=B] DC-081: Input validation for 20 highest-risk mutating routes

Secures 20 mutating routes across 7 files against path traversal, shell
injection, and ReDoS vectors:
- containers.js: container ID validation + resource limit bounds (6 routes)
- recipes/manage.js: recipe ID slug validation (4 routes)
- tailscale.js: subdomain regex before interpolation + shell char blocking (2)
- workflows.js: workflow ID slug validation (3 routes)
- dependencies.js: service ID + dependsOn array validation (3 routes)
- logs.js: YYYY-MM-DD date format validation (1 route)
- sites.js: additional domain validation (1 route)

Uses existing REGEX patterns from constants.js. No new dependencies.
Codex: B (no blocking issues, 4 Low follow-ups for tests + strict bools).
1552/1552 tests pass, 0 regressions.

dashcaddy-api/routes/recipes/manage.js

@@ -1,8 +1,23 @@
 const express = require('express');
 const { DOCKER } = require('../../src/utilities/constants');
-const { NotFoundError } = require('../../src/utilities/errors');
+const { NotFoundError, ValidationError } = require('../../src/utilities/errors');
 const { ok } = require('../../src/utils/responses');
 
+/**
+ * Validate a recipe ID for use in Docker label filters.
+ * @param {string} recipeId - Recipe ID from route param
+ * @throws {ValidationError} if the ID contains unsafe characters
+ */
+function validateRecipeId(recipeId) {
+  if (!recipeId || typeof recipeId !== 'string') {
+    throw new ValidationError('Recipe ID is required');
+  }
+  // Recipe IDs are slug-style: lowercase letters, numbers, hyphens
+  if (!/^[a-zA-Z0-9][a-zA-Z0-9_-]{0,63}$/.test(recipeId)) {
+    throw new ValidationError('Invalid recipe ID format');
+  }
+}
+
 module.exports = function({ servicesStateManager, asyncHandler, log, docker, notification, buildDomain, caddy }) {
   const router = express.Router();
 
@@ -107,6 +122,7 @@ module.exports = function({ servicesStateManager, asyncHandler, log, docker, not
    */
   router.post('/:recipeId/start', asyncHandler(async (req, res) => {
     const { recipeId } = req.params;
+    validateRecipeId(recipeId);
     const containers = await findRecipeContainers(recipeId);
 
     if (containers.length === 0) {
@@ -138,6 +154,7 @@ module.exports = function({ servicesStateManager, asyncHandler, log, docker, not
    */
   router.post('/:recipeId/stop', asyncHandler(async (req, res) => {
     const { recipeId } = req.params;
+    validateRecipeId(recipeId);
     const containers = await findRecipeContainers(recipeId);
 
     if (containers.length === 0) {
@@ -170,6 +187,7 @@ module.exports = function({ servicesStateManager, asyncHandler, log, docker, not
    */
   router.post('/:recipeId/restart', asyncHandler(async (req, res) => {
     const { recipeId } = req.params;
+    validateRecipeId(recipeId);
     const containers = await findRecipeContainers(recipeId);
 
     if (containers.length === 0) {
@@ -196,6 +214,7 @@ module.exports = function({ servicesStateManager, asyncHandler, log, docker, not
    */
   router.delete('/:recipeId', asyncHandler(async (req, res) => {
     const { recipeId } = req.params;
+    validateRecipeId(recipeId);
     const containers = await findRecipeContainers(recipeId);
 
     if (containers.length === 0) {