Build a free, no-code live subscriber counter in under 5 minutes.

Build me a single self-contained index.html file that displays my live YouTube subscriber count full-screen.

Requirements:
- Uses the YouTube Data API v3 (channels.list, part=statistics)
- Reads my API key and Channel ID from two constants at the top of the file
- Fills the entire browser viewport, perfectly centered
- Huge subscriber number (responsive font-size using clamp())
- Black background, bright red number, white channel name above it
- Auto-refreshes every 30 seconds without flicker
- Animated count-up when the number changes
- Clean, no external libraries, no build step

Output only the complete HTML in one code block.

Update the file so:
- Background is a subtle dark gradient (top: #0a0a0a, bottom: #1a1a1a)
- The number uses a custom Google Font (Inter, weight 900)
- Add my channel name "@ChadSheppardAI" above the number in 0.4em size
- Add a small caption below the number: "Goal: 100,000"
- Show a thin progress bar under the goal text representing current / 100000

Add a second line below the subscriber number that shows:
- How many subscribers I need to reach 100,000
- The percentage complete toward that goal
- Animate the progress bar smoothly when the number updates

Take the same file and swap the data source. Instead of YouTube subscribers, fetch [STRIPE REVENUE / STOCK PRICE / STEP COUNT / WEBSITE VISITORS] from [API ENDPOINT]. Keep the same full-screen layout, animation, and styling. Tell me exactly where to paste my API credentials.