fix: favicon SVG — remplace le 404 favicon.ico

- SVG 32×32: fond bleu accent #2383E2, texte 'FD' blanc, coins arrondis
- Ajouté <link rel=icon type=image/svg+xml> dans <head> de base.html
- Fichier static/favicon.svg servi via le mount /static existant

app/templates/base.html

@@ -4,6 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>FlowDeck</title>
+  <link rel="icon" type="image/svg+xml" href="/static/favicon.svg">
   <link rel="stylesheet" href="/static/css/app.css">
   <script src="https://unpkg.com/[email protected]"></script>
   <script src="https://unpkg.com/[email protected]" defer></script>

static/favicon.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect width="32" height="32" rx="6" fill="#2383E2"/>
+  <text x="16" y="22" text-anchor="middle" font-family="Arial,sans-serif" font-size="16" font-weight="bold" fill="#fff">FD</text>
+</svg>