feat: card UI polish — voting pill, rank badge, selection, density

Rework card layout from flex to block flow for sidebar compatibility.
Add voting pill capsule with voted-state tinting (orange/purple),
rank badge watermark, custom rt-selected selection system replacing
Reddit/RES classes, density-responsive border radius, bold titles,
and comprehensive dark mode variants for all interactive states.

Co-authored-by: Cursor <cursoragent@cursor.com>

content/tweaks/cards.js

@@ -4,6 +4,12 @@
   function processPost(post) {
     if (post.classList.contains("rt-card")) return;
     post.classList.add("rt-card");
+
+    var rank = post.querySelector(":scope > .rank");
+    if (rank) {
+      rank.classList.add("rt-rank-badge");
+      post.appendChild(rank);
+    }
   }
 
   function processPosts() {
@@ -36,17 +42,44 @@
     }
   }
 
+  var DENSITY_CLASSES = ["rt-density-cozy", "rt-density-modern", "rt-density-extra"];
+
+  function applyDensity(settings) {
+    var html = document.documentElement;
+    for (var i = 0; i < DENSITY_CLASSES.length; i++) {
+      html.classList.remove(DENSITY_CLASSES[i]);
+    }
+    var cls = "rt-density-" + (settings.cardDensity || "modern");
+    html.classList.add(cls);
+  }
+
+  function initSelection() {
+    document.addEventListener("mousedown", function (e) {
+      var clickedCard = e.target.closest(".rt-card");
+      var prev = document.querySelectorAll(".rt-card.rt-selected");
+      for (var i = 0; i < prev.length; i++) {
+        prev[i].classList.remove("rt-selected");
+      }
+      if (clickedCard) {
+        clickedCard.classList.add("rt-selected");
+      }
+    });
+  }
+
   function apply(settings) {
     document.documentElement.classList.add("rt-card-enabled");
     applyDarkMode(settings);
     applyBackground(settings);
+    applyDensity(settings);
     applyGap(settings);
     processPosts();
+    initSelection();
   }
 
   function updateSettings(settings) {
     applyDarkMode(settings);
     applyBackground(settings);
+    applyDensity(settings);
     applyGap(settings);
   }