fix: SearXNG startup + update README logo and favicon

- Fix SearXNG limiter.toml directory issue by creating file at container
  startup via entrypoint command (rm -rf then recreate)
- Update README to use logo.svg instead of logo.png
- Redesign favicon.svg to match main logo style:
  - Same gold-to-green gradient background
  - Line gradient from white to green
  - Glow effect on chart line
  - Decorative dots at data points
  - Green arrow indicator

README.md

@@ -1,11 +1,11 @@
 <p align="center">
-  <img src="frontend/public/logo.png" alt="PriceFlow logo" width="100">
+  <img src="frontend/public/logo.svg" alt="PriceFlow logo" width="120">
 </p>
 
 <h1 align="center">PriceFlow</h1>
 
 <p align="center">
-  <strong>Suivi de prix intelligent propulsé par l'IA</strong>
+  <strong>Suivi de prix intelligent propulse par l'IA</strong>
 </p>
 
 <p align="center">