feat: add Figlet ASCII art generator as 7th tool

- Added Figlet tool with 373 fonts for ASCII art text generation
- Created new gradient-yellow-amber for terminal/retro aesthetic
- Updated Stats component from 6 to 7 tools
- Updated Footer badge to 7 tools and added Figlet link
- Added Figlet to README Available Tools section

Figlet Features:
- 373 curated fonts from xero/figlet-fonts collection
- Live preview and fuzzy search
- Multiple export formats (text, PNG, SVG, code snippets)
- Shareable URLs and keyboard shortcuts
- Perfect for ASCII banners, terminal art, and retro designs

Color: Yellow (#eab308) to Amber (#f59e0b) gradient
URL: https://figlet.kit.pivoine.art

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/globals.css

@@ -102,3 +102,7 @@ body {
 @utility gradient-indigo-purple {
   background: linear-gradient(135deg, #6366f1 0%, #a855f7 100%);
 }
+
+@utility gradient-yellow-amber {
+  background: linear-gradient(135deg, #eab308 0%, #f59e0b 100%);
+}