fix: Replace ALL remaining hardcoded #ddd borders with theme variable

Replaced 12 hardcoded borders across 5 files:
- _cv-section.css: 2 borders (company icons)
- _projects.css: 2 borders (project icons)
- _courses.css: 2 borders (course icons)
- _toggles.css: 3 borders (logo containers)
- logo-toggle.css: 3 borders (logo containers)

All icon borders now use var(--icon-border):
- Light theme: #ddd (visible)
- Dark theme: transparent (invisible)

Verified with Playwright: rgba(0,0,0,0) in dark theme

static/css/03-components/_cv-section.css

@@ -249,7 +249,7 @@
     height: 60px;
     object-fit: contain;
     border-radius: 4px;
-    border: 1px solid #ddd;
+    border: 1px solid var(--icon-border);
     background: transparent;
     padding: 4px;
 }
@@ -261,7 +261,7 @@
     align-items: center;
     justify-content: center;
     border-radius: 4px;
-    border: 1px solid #ddd;
+    border: 1px solid var(--icon-border);
     background: transparent;
     color: var(--text-light);
     padding: 8px;