Tier cards: add navy-pill buy CTAs per policy

Each live tier card now ends in a navy-950 pill linking to
licensing.keysat.xyz/buy/keysat?policy=<slug>. margin-top:auto on
the CTA anchors it to the bottom of each card so buttons line up
across tiers of different heights.

index.html

@@ -360,6 +360,17 @@ pre.code .p { color:rgba(245,241,232,0.55); }
   text-decoration:line-through; text-decoration-color:rgba(14,31,51,0.4);
 }
 .tier-card .tier-features-list { margin-top:4px; }
+.tier-card .tier-buy-cta {
+  display:block; margin-top:auto;
+  align-self:stretch; text-align:center;
+  padding:12px 22px; border-radius:999px;
+  background:var(--navy-950); color:var(--cream-50);
+  font-family:var(--font-display); font-weight:600; font-size:14px;
+  letter-spacing:-0.005em; text-decoration:none;
+  transition:background 100ms;
+}
+.tier-card .tier-features-list { margin-bottom:18px; }
+.tier-card .tier-buy-cta:hover { background:var(--navy-800); }
 
 /* ---------- Install ---------- */
 .install-grid { display:grid; grid-template-columns:1fr 1fr; gap:24px; }
@@ -1249,6 +1260,14 @@ fmt.<span class="f">Printf</span>(<span class="s">"licensed for %s, expires %s\n
       });
       card.appendChild(list);
     }
+    // Buy CTA — navy pill that links to the master Keysat's buy page
+    // with the right policy slug pre-selected. Free tier links to the
+    // same page; it renders "Redeem license" automatically.
+    const buyBtn = document.createElement('a');
+    buyBtn.className = 'tier-buy-cta';
+    buyBtn.href = KEYSAT_API + '/buy/' + PRODUCT_SLUG + '?policy=' + encodeURIComponent(pol.slug);
+    buyBtn.textContent = 'Get ' + pol.name;
+    card.appendChild(buyBtn);
     return card;
   }