feat: add --watch/-w flag for live system monitoring dashboard

[h4sht]

Summary

This PR adds a --watch mode that turns fastfetch into a live-updating system monitor — perfect for keeping an eye on your system in real-time.

🎬 Demo

# Watch with default 2-second interval
fastfetch --watch

# Watch with custom 1-second interval
fastfetch --watch 1000

# Short flag
fastfetch -w 500

✨ Features

• --watch [interval_ms] flag (short: -w, default: 2000ms)
• Reverse-video header bar showing:
  • Current timestamp
  • Iteration count (Segmentation fault (core dumped) #1, [Bug] Distro logo getting cut off when reducing the amount of information printed #2, Add support for Artix #3...)
  • Refresh interval
  • "Ctrl+C to exit" hint
• Clean alternate buffer mode — no terminal scroll spam
• Built on existing --dynamic-interval infrastructure

📸 Screenshot description

When running fastfetch --watch, the terminal enters a full-screen alternate buffer with:

• A highlighted status bar at the top
• Your normal fastfetch output below
• Auto-refreshing at the configured interval
• Clean exit with Ctrl+C

🔧 Implementation

• Added printWatchHeader() function using existing ffTimeToShortStr() / ffTimeGetNow() for cross-platform time formatting
• --watch flag in parseCommand() maps to dynamicInterval internally
• Iteration counter and header printed after each \e[H cursor-home in the main loop

Files changed

• src/fastfetch.c: Added printWatchHeader(), --watch/-w parsing, iteration counter

[CarterLi]

This doesn't seem correct to me.

In addition, the --watch flag basically does the same thing with --dynamic-interval, I think keeping one of them is enough.

Thank you and your AI agent for other PRs BTW.