feat(integration): add docs/visio logos, theme.css, and nginx updates

Add SVG logos for docs and visio apps. Update drive, mail, people logos.
Add theme.css served at /api/v2/theme.css for La Suite frontend theming.
Update nginx to serve theme endpoint and tighten cache headers.
Update Dockerfile to include new static assets.

logos/visio.svg

@@ -0,0 +1,9 @@
+<svg width="48" height="48" viewBox="0 0 48 48" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <!-- Camera body -->
+  <rect x="4" y="14" width="28" height="20" rx="3" fill="#f59e0b"/>
+  <!-- Camera lens -->
+  <circle cx="18" cy="24" r="6" fill="#d97706"/>
+  <circle cx="18" cy="24" r="3" fill="#f59e0b"/>
+  <!-- Play triangle (video) -->
+  <path d="M36 16l8 8-8 8V16z" fill="#d97706"/>
+</svg>