fix: UAC elevation, script encoding, MySQL Workbench URL

- main.ts: Start-Process -Verb RunAs incompatible with -RedirectStandardOutput/Error on Windows. Pipe through Tee-Object inside elevated context instead.
- 20 installer scripts: replace em-dash/ellipsis/smart-quotes with ASCII. PowerShell 5.1 reads UTF-8-no-BOM as CP1252, corrupting non-ASCII bytes and breaking string terminators.
- install-mysql-workbench.ps1: dev.mysql.com/get/ redirect returns Oracle firewall page (fw_error_www). Switch to cdn.mysql.com direct with multi-version fallback.
- Bump 1.2.0 -> 1.2.1

Initial commit: DevTools Hub app & installers

Electron + React + TypeScript app for installing and managing dev tools on Windows, macOS, and Linux.

Features: - Installer UI with tool selection, progress tracking, and real-time logs
  - Dashboard showing install status and versions for all registered tools
  - PowerShell/Bash installer scripts with direct official downloads (no winget/brew dependency)
  - Automatic PATH configuration per tool and per OS
  - RTK (Rust Token Killer) integration with config modal
  - Support for 25+ tools: Git, Node.js, Python, Go, Java, Deno, Bun, Rust,
    Docker, PostgreSQL, MongoDB, Redis, VSCode, Postman, phpMyAdmin, and more

Stack: Electron, React, TypeScript, Vite, TailwindCSS