refactor: professional restructuring, modular plugin system, and high-performance brute-force integration

[PNP-MA]

This PR represents a major evolution of DarkScout, transforming it from a simple script into a professional, modular framework for
subdomain enumeration. The architecture has been completely overhauled to follow SOLID principles, DRY patterns, and modern Rust best
practices.

🚀 Key Changes

• Professional Folder Restructuring: Organized the codebase into dedicated modules (plugins, models, io, utils, browser, bruteforce,
  args, errors) to ensure high maintainability and a clean src root.
• Modular Plugin System: Introduced a trait-based Plugin system with a centralized PluginRegistry. This allows for seamless integration
  of new OSINT sources.
• High-Performance Brute Force: Integrated a new asynchronous brute-force engine using trust-dns-resolver and tokio::sync::Semaphore for
  ultra-fast, thread-safe DNS resolution with controlled concurrency.
• Advanced Error Handling: Replaced generic error types with a structured DarkScoutError enum using the thiserror crate, providing
  context-aware feedback for network, parsing, and authentication issues.
• Polished UI/UX:
  • Concurrent MultiProgress bars for simultaneous plugin execution.
  • Professional terminal styling using console (colors, emojis, and a modern ASCII logo).
  • Clean, deduplicated, and sorted final results output.
• Enhanced CLI Interface:
  • -p / --plugins: Select specific plugins to run.
  • -l / --list: List all available plugins and their current status (enabled/disabled).
  • -w / --wordlist: Support for single files, multiple files, or entire directories for brute forcing.
  • -c / --concurrency: User-defined concurrency levels for brute-forcing.
• New OSINT Sources: Added WaybackArchive and BeVigil plugins to expand discovery capabilities.
• Request Centralization: Created a Browser module to manage reqwest clients, headers (User-Agents), and timeouts consistently across all
  plugins.

🛠️ Technical Improvements

• Concurrency Control: Implemented a Semaphore to limit concurrent plugins to 3 at a time, preventing terminal flickering and redraw
  artifacts.
• Deduplication: Added a rigorous normalization and deduplication pipeline to ensure unique, clean results.
• Production Ready: Fixed all compiler warnings (dead_code, unused_imports) and updated .gitignore and README.md to professional
  standards.

✅ Verification

• Successfully tested full scans on google.com and hackthissite.org.
• Verified individual plugin execution and error handling.
• cargo check and cargo build run with 0 warnings/errors.