Add rate limiting, cron scheduling, webhooks, dry-run, execution filtering, and UX improvements

- Rate limiting: 300 req/15min general, 20 req/min on POST /api/executions
- Cron schedule type support using cron-parser for full cron expressions
- Webhook notifications: POST to workflow webhook_url on execution complete/failed
- Dry-run mode: simulate workflow execution without running any commands
- Global execution timeout via EXECUTION_MAX_MINUTES env var (default 60min)
- Execution filtering: status, workflow_id, started_by, after, before, search
- Event-driven command result delivery (replaces 500ms DB polling)
- Atomic log appends via JSON_ARRAY_APPEND (no read-modify-write race)
- Separate browserClients/workerClients sets (workers no longer receive broadcasts)
- Stale execution cleanup on startup (mark running→failed after crash)
- Scheduler overlap prevention (skip if same workflow already running)
- Frontend: webhook_url field in create/edit workflow modals
- Frontend: dry-run checkbox in workflow param modal
- Frontend: ESC closes modals, ws.onerror handler added
- Frontend: selectedExecutions changed from Array to Set (O(1) ops)
- Frontend: XSS fixes via escapeHtml() on all user-controlled innerHTML
- Frontend: param modal keydown listener deduplication fix
- Remove unused npm packages (bcryptjs, body-parser, cors, js-yaml, jsonwebtoken)
- Add express-rate-limit and cron-parser dependencies

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

package-lock.json

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       "version": "1.0.0",
       "license": "ISC",
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         "dotenv": "^17.2.3",
         "express": "^5.1.0",
+        "express-rate-limit": "^8.3.1",
         "mysql2": "^3.15.3",
         "ws": "^8.18.3"
       }
@@ -139,6 +141,17 @@
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@@ -302,6 +315,23 @@
         "url": "https://opencollective.com/express"
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+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/express-rate-limit"
+      },
+      "peerDependencies": {
+        "express": ">= 4.11"
+      }
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     "node_modules/finalhandler": {
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       "license": "ISC"
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+    "node_modules/ip-address": {
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+      "resolved": "https://registry.npmjs.org/ip-address/-/ip-address-10.1.0.tgz",
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     "node_modules/ipaddr.js": {
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@@ -521,6 +559,14 @@
         "url": "https://github.com/sponsors/wellwelwel"
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+    "node_modules/luxon": {
+      "version": "3.7.2",
+      "resolved": "https://registry.npmjs.org/luxon/-/luxon-3.7.2.tgz",
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