feat: Interactive setup wizard (install.sh --interactive)

[Hrithik-Gavankar]

Summary

Add an interactive mode to the installer that walks users through configuration step-by-step with prompts, validation, and auto-detection where possible.

Motivation

• Current setup requires manually editing multiple files
• New users might miss configuration steps
• Auto-detection can fill in most fields without manual input

Proposed Flow

$ bash install.sh --interactive

🧠 Engineer Brain — Interactive Setup
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

? Which AI assistant do you use?
  ❯ Cursor
    Claude Code
    VS Code Copilot
    Windsurf
    Aider
    Continue.dev

? Where is your workspace? (auto-detected: ~/Development)
  ~/Development

? What's your git author name/email? (auto-detected: Jane Engineer <jane@company.com>)
  jane\|jane@company

? Your name: Jane Engineer
? Your role: Senior Software Engineer
? Your company: Acme Corp
? Years of experience: 6
? Career goal: Staff Engineer

✅ Installed for: Cursor
✅ Scanner configured: ~/Development, author=jane|jane@company
✅ Context file populated with your details
✅ BRAIN.md template ready

Next: Open your AI assistant and say "engineer-brain update"

Features

• Platform selection menu
• Auto-detect workspace path (cwd or common paths)
• Auto-detect git author from git config user.name / user.email
• Guided context file population (name, role, skills, goals)
• Validation (check paths exist, git repos found)
• Dry-run mode (--dry-run to preview without writing)
• Colorized terminal output with progress indicators