Landing: add the symmetry video

index.html

@@ -50,6 +50,9 @@ a.card p{margin:0;color:var(--muted);font-size:12.5px}
       <span class="go">open overlays →</span>
     </a>
   </div>
+  <h2 style="font-family:var(--display);font-weight:500;font-size:28px;margin:8px 0 0">Symmetry costs a line</h2>
+  <p class="lede">Force up–down mirror symmetry on the yantra while keeping all 29 triple points exact, and two of its bases are pulled into one line, carrying one point on the axis and a mirror pair: 1 + 2.</p>
+  <video controls playsinline preload="none" src="https://teahub.xyz/maths/videos/raw/commit/a7601b040a95725e40e58f6ac214a2fe096a3a3e/yantra-symmetry.mp4"></video>
   <section class="notes">
     <p><span class="dot" style="background:var(--up)"></span>four upward triangles · <span class="dot" style="background:var(--down)"></span>five downward · <span class="dot" style="background:var(--bindu)"></span>the bindu</p>
     <p>Triangle coordinates follow a numerical solution of the yantra's concurrency conditions (after Kulaichev and Huet), drawn as 27 lines with 29 triple points.</p>