feat: import existing gitea customizations from mvpsm

Themes (dark/light), logo, favicon, and template overrides.

templates/custom/header.tmpl

@@ -0,0 +1,40 @@
+<style>
+  /* mGit Branding and Typography */
+  @import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap');
+  
+  /* Logo styling for mGit */
+  .ui.menu .item img.logo {
+    height: 36px;
+    width: auto;
+    margin-right: 8px;
+  }
+  
+  /* mGit text logo styling */
+  .ui.menu .item .mgit-logo-text {
+    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+    font-weight: 700;
+    font-size: 1.5rem;
+    letter-spacing: -0.03em;
+    color: var(--color-text, #1e293b);
+    text-decoration: none;
+    display: inline-flex;
+    align-items: center;
+    gap: 0.5rem;
+  }
+  
+  /* Subtle top border accent */
+  body {
+    border-top: 3px solid var(--color-primary, #2563eb);
+  }
+  
+  /* Header menu improvements */
+  .ui.menu {
+    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+    font-weight: 500;
+  }
+  
+  /* Improve readability */
+  .ui.menu .item {
+    letter-spacing: -0.01em;
+  }
+</style>