fix: Correct signal strength CSS class names to match JavaScript - resolves #12

Changed CSS class names from 'rssi-*' to 'signal-*' to match the naming
used in JavaScript code (ui-manager.js:187-190). This fixes signal strength
color indicators that were not displaying properly due to the mismatch.

Signal strength colors now work correctly:
- signal-strong: bright green (#00ff88)
- signal-good: yellow (#ffff00)
- signal-weak: orange (#ff8c00)
- signal-poor: red (#ff4444)

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

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

assets/static/css/style.css

@@ -374,10 +374,10 @@ body {
 .type-badge.ground { background: #888888; color: #ffffff; }
 
 /* RSSI signal strength colors */
-.rssi-strong { color: #00ff88; }
-.rssi-good { color: #ffff00; }
-.rssi-weak { color: #ff8c00; }
-.rssi-poor { color: #ff4444; }
+.signal-strong { color: #00ff88; }
+.signal-good { color: #ffff00; }
+.signal-weak { color: #ff8c00; }
+.signal-poor { color: #ff4444; }
 
 .stats-grid {
     display: grid;