refactor: every project landing has its own theme

- landing.css is layout only and uses tokens (colors, fonts, hero, nav)
- palettes live in css/landing-<theme>.css; Robotex gets its own dark
  theme, MyPointVPN sets the same tokens
- theme defaults to the project folder name; the build fails if the
  theme file is missing, so a landing can't ship without styles

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

assets/css/landing-mypointvpn.css

@@ -11,8 +11,19 @@
   --accent-strong: #0a6e4c;
   --lime: #c8f169;
   --ink: #0f1a16;
+  --surface-hover: #fff;
+  --accent-soft: rgba(13, 138, 95, .1);
+  --accent-line: var(--accent);
+  --on-accent: #fff;
+  --code-bg: #0f1a16;
+  --code-text: #e9f1ec;
+  --nav-bg: rgba(246, 244, 238, .85);
+  --hero-bg:
+    radial-gradient(40rem 26rem at 85% 20%, rgba(200, 241, 105, .45), transparent 70%),
+    var(--bg);
   --radius: 1.1rem;
-  font-family: 'Manrope', system-ui, sans-serif;
+  --font: 'Manrope', system-ui, sans-serif;
+  --font-mono: 'JetBrains Mono', monospace;
 }
 .theme-mypointvpn h1,
 .theme-mypointvpn h2 { font-family: 'Unbounded', 'Manrope', sans-serif; font-weight: 700; letter-spacing: -.01em; }
@@ -20,7 +31,6 @@
 .theme-mypointvpn code { background: rgba(13, 138, 95, .1); padding: .05em .35em; border-radius: .35em; font-size: .9em; }
 
 /* nav */
-.theme-mypointvpn .nav { background: rgba(246, 244, 238, .85); }
 .theme-mypointvpn .nav__logo { font-family: 'Unbounded', sans-serif; font-weight: 700; }
 .theme-mypointvpn .nav__logo::before {
   content: ""; display: inline-block; width: .6rem; height: .6rem; margin-right: .5rem;
@@ -31,9 +41,6 @@
 /* hero: text left, chat right */
 .theme-mypointvpn .hero {
   text-align: left;
-  background:
-    radial-gradient(40rem 26rem at 85% 20%, rgba(200, 241, 105, .45), transparent 70%),
-    var(--bg);
 }
 .theme-mypointvpn .hero--split .wrap {
   display: grid; grid-template-columns: 1.15fr 1fr; gap: 3rem; align-items: center;
@@ -43,7 +50,6 @@
 .theme-mypointvpn .hero__cta { justify-content: flex-start; }
 .theme-mypointvpn .badge { border-color: var(--accent); color: var(--accent-strong); background: var(--surface); }
 .theme-mypointvpn .btn { background: var(--surface); border-color: var(--border); color: var(--text); border-radius: 999px; }
-.theme-mypointvpn .btn:hover { background: #fff; }
 .theme-mypointvpn .btn--primary { background: var(--ink); border-color: var(--ink); color: var(--lime); }
 .theme-mypointvpn .btn--primary:hover { background: var(--accent-strong); color: #fff; }
 @media (max-width: 820px) {