refactor(bidding): extract CSS and reorganize file structure

Refactored the bidding application by reorganizing the file structure and extracting CSS into separate files.

- The monolithic `control.html` and `display.html` files have been moved into dedicated `controls/` and `display/`
directories.
- All inline CSS has been extracted into component-specific `style.css` files.
- A new `common/style.css` has been created to hold shared styles, promoting reusability and reducing duplication.

These changes improve the project's modularity, separation of concerns (HTML/CSS), and long-term maintainability without
affecting external behavior.

bidding/common/style.css

@@ -0,0 +1,48 @@
+:root {
+  --primary: #2563eb;
+  --primary-dark: #1d4ed8;
+  --accent: #ffd700;
+  --accent-green: #00c853;
+  --dark-1: #111827;
+  --dark-2: #1f2937;
+  --dark-3: #374151;
+  --light: #f9fafb;
+  --text-primary: #f3f4f6;
+  --text-secondary: #d1d5db;
+  --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
+  --shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.5);
+  --radius: 16px;
+}
+
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+body {
+  font-family: "Inter", sans-serif;
+  background: linear-gradient(135deg, var(--dark-1) 0%, var(--dark-2) 100%);
+  color: var(--text-primary);
+  padding: 20px;
+  min-height: 100vh;
+}
+
+.container {
+  max-width: 1200px;
+}
+
+.card {
+  background: rgba(31, 41, 55, 0.8);
+  backdrop-filter: blur(10px);
+  border-radius: var(--radius);
+  box-shadow: var(--shadow);
+  border: 1px solid rgba(255, 255, 255, 0.1);
+  transition: var(--transition);
+}
+
+h1 {
+  background: linear-gradient(90deg, var(--primary) 0%, var(--accent) 100%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+}