feat(frontend): Kinetic Precision design system — new lime theme, glassmorphism, redesigned pages

- New design system: Stitch (kinetic-precision.css) with lime (#cafd00) accent
- New Google Fonts: Lexend, Plus Jakarta Sans, Space Grotesk
- New page: BenchmarksPage with strength/endurance/body tracking
- Redesigned: Dashboard, ProgressPage, WorkoutPage, LoginPage + LoginPage.css
- Add shared glassmorphism nav, kinetic buttons, intensity indicators
- Build: 265KB JS / 88KB CSS / 2.54s (clean)

frontend/nginx.conf

@@ -20,12 +20,20 @@ server {
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     }
 
+    # index.html — never cache so new deploys load fresh
+    location = /index.html {
+        try_files $uri /index.html;
+        add_header Cache-Control "no-store, no-cache, must-revalidate";
+        add_header Pragma "no-cache";
+        expires 0;
+    }
+
     # SPA fallback
     location / {
         try_files $uri $uri/ /index.html;
     }
 
-    # Cache static assets
+    # Cache static assets (fingerprinted filenames, safe to cache long)
     location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2)$ {
         expires 1y;
         add_header Cache-Control "public, immutable";