docs: add VIGIL showcase page (vigil.netslum.io)

Static landing page reusing the OVERWATCH/SKELETONKEY design system:
hero + main-screen screenshot, the five tracker ecosystems, the
co-movement decision model + OBSERVED/SUSPICIOUS/ALERTING tiers, the
rotating-clone problem, and the fully-offline privacy story.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/app.js

@@ -0,0 +1,46 @@
+/* OVERWATCH landing — count-up stats + scroll reveal. No network, no deps. */
+(function () {
+  'use strict';
+  const reduceMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
+
+  /* count-up numbers when the stats row scrolls into view */
+  function countUp(el) {
+    const target = parseInt(el.dataset.target, 10);
+    if (isNaN(target)) return;
+    if (!target || reduceMotion) { el.textContent = String(target); return; }
+    const dur = 1100, start = performance.now();
+    (function tick(now) {
+      const p = Math.min(1, (now - start) / dur);
+      el.textContent = String(Math.round(target * (1 - Math.pow(1 - p, 3))));
+      if (p < 1) requestAnimationFrame(tick);
+    })(performance.now());
+  }
+
+  const statsRow = document.getElementById('stats-row');
+  if (statsRow) {
+    const nums = statsRow.querySelectorAll('.num[data-target]');
+    if ('IntersectionObserver' in window && !reduceMotion) {
+      const io = new IntersectionObserver((entries, obs) => {
+        entries.forEach((e) => {
+          if (e.isIntersecting) { nums.forEach(countUp); obs.disconnect(); }
+        });
+      }, { threshold: 0.4 });
+      io.observe(statsRow);
+    } else {
+      nums.forEach((el) => { el.textContent = el.dataset.target; });
+    }
+  }
+
+  /* scroll-triggered reveal */
+  const reveals = document.querySelectorAll('.reveal');
+  if (!('IntersectionObserver' in window) || reduceMotion) {
+    reveals.forEach((el) => el.classList.add('in'));
+  } else {
+    const ro = new IntersectionObserver((entries, obs) => {
+      entries.forEach((e) => {
+        if (e.isIntersecting) { e.target.classList.add('in'); obs.unobserve(e.target); }
+      });
+    }, { threshold: 0.12, rootMargin: '0px 0px -40px 0px' });
+    reveals.forEach((el) => ro.observe(el));
+  }
+})();