Design overhaul: Dark fitness theme, no emojis

CSS:
- Dark background (#0a0a0f, #0d0d12, #15151b)
- Orange accent (#ff6b35)
- Muted text (#a1a1aa, #71717a)
- Inter font from Google Fonts
- Workout type colors (push/pull/legs/etc)

Dashboard:
- Calendar dots are CSS circles, not emoji
- Coach avatar uses SVG icon
- All emojis replaced with Icons.jsx SVGs
- Navigation uses proper icons

WorkoutPage:
- Warmup exercises without emojis
- Check icons instead of emoji checkmarks
- Arrow icons for navigation
- Fire icon for warmup section

Professional fitness app aesthetic inspired by Nike/FITBOD

frontend/src/index.css

@@ -5,21 +5,43 @@
 }
 
 :root {
-  --bg-primary: #0f0f1a;
-  --bg-secondary: #1a1a2e;
-  --bg-card: #16213e;
-  --bg-card-hover: #1f3460;
-  --text-primary: #eaeaea;
-  --text-secondary: #a0a0a0;
-  --accent: #e94560;
-  --accent-hover: #ff6b6b;
-  --success: #4ecca3;
-  --warning: #ffd93d;
-  --border: #2a2a4a;
+  /* Dark fitness palette */
+  --bg-primary: #0a0a0f;
+  --bg-secondary: #0d0d12;
+  --bg-card: #15151b;
+  --bg-card-hover: #1a1a22;
+  --bg: #0a0a0f;
+
+  /* Text colors */
+  --text-primary: #ffffff;
+  --text-secondary: #a1a1aa;
+  --text-muted: #71717a;
+  --text: #ffffff;
+
+  /* Accent - energetic orange */
+  --accent: #ff6b35;
+  --accent-hover: #ff8555;
+
+  /* Status colors */
+  --success: #22c55e;
+  --warning: #f59e0b;
+  --error: #ef4444;
+
+  /* Border */
+  --border: #1f1f28;
+
+  /* Workout type colors - muted, professional */
+  --workout-push: #ef4444;
+  --workout-pull: #3b82f6;
+  --workout-legs: #22c55e;
+  --workout-shoulders: #f59e0b;
+  --workout-upper: #8b5cf6;
+  --workout-lower: #06b6d4;
+  --workout-default: #ff6b35;
 }
 
 html, body {
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
+  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
   background: var(--bg-primary);
   color: var(--text-primary);
   min-height: 100vh;
@@ -27,6 +49,10 @@ html, body {
   -moz-osx-font-smoothing: grayscale;
 }
 
+h1, h2, h3, h4, h5, h6 {
+  font-weight: 700;
+}
+
 #root {
   min-height: 100vh;
 }