Security hardening, bug fixes, and performance improvements

Security fixes:
- Replace new Function() condition eval with vm.runInNewContext() (RCE fix)
- Add admin checks to DELETE executions, all scheduled-commands endpoints
- Remove api_key from GET /api/workers response (was exposed to all employees)
- Separate browserClients/workerClients sets; broadcast() now sends to browsers only
- Add worker WebSocket auth: reject if api_key provided but invalid
- Fix XSS: escapeHtml() on step_name, duration, worker_id, user info, execution_id

Bug fixes:
- Replace DB-polling waitForCommandResult with event-driven _commandResolvers Map
- Replace non-atomic addExecutionLog with JSON_ARRAY_APPEND (fixes concurrent write race)
- Add stale execution recovery on startup: running→failed with log entry
- Fix calculateNextRun returning null for unknown types (now throws)
- Fix scheduler overlap: skip if previous execution still running
- Fix JSON double-parse on worker_ids column
- Fix switchTab() bare event.target reference
- Fix selectedExecutions Array→Set (O(1) lookups, fixes performance regression)
- Fix param modal event listener leak (delegated handler, removes before re-adding)
- Add ws.onerror handler (was silently swallowing WebSocket errors)
- Move misplaced routes to before server.listen()

Performance/cleanup:
- DB connection pool 10→50
- EXECUTION_RETENTION_DAYS default 1→30 (matches docs)
- Remove unused packages: bcryptjs, body-parser, cors, js-yaml, jsonwebtoken
- Remove generateUUID() wrapper, use crypto.randomUUID() directly
- Remove dead example workflow constants
- Add ESC key handler to close modals
- Fix clearCompletedExecutions limit 1000→9999
- Add security notice to README.md

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

README.md

@@ -2,6 +2,8 @@
 
 A distributed workflow orchestration platform for managing and executing complex multi-step operations across server clusters through a retro terminal-themed web interface.
 
+> **Security Notice:** This repository is hosted on Gitea and is version-controlled. **Never commit secrets, credentials, passwords, API keys, or any sensitive information to this repo.** All sensitive configuration belongs exclusively in `.env` files which are listed in `.gitignore` and must never be committed. This includes database passwords, worker API keys, webhook secrets, and internal IP details.
+
 ## Overview
 
 PULSE is a centralized workflow execution system designed to orchestrate operations across distributed infrastructure. It provides a powerful web-based interface with a vintage CRT terminal aesthetic for defining, managing, and executing workflows that can span multiple servers, require human interaction, and perform complex automation tasks at scale.