refactor: clean up themes, templates, and add comprehensive README

- Themes now only override CSS variables (no selector overrides)
- Removed duplicate styles from header.tmpl (just loads Inter font now)
- Cleaned up logo SVG (simpler, no overlapping text)
- Improved home page with proper hero layout and sign-in/explore buttons
- Added detailed README documenting the setup, deployment, and design principles

templates/custom/header.tmpl

@@ -1,40 +1,3 @@
-<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>
+<link rel="preconnect" href="https://fonts.googleapis.com">
+<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
+<link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap" rel="stylesheet">