Replace abandoned spatie/commonmark-highlighter with tempest/highlight

Swap the syntax highlighting library and its CSS theme (zenburn -> nord,
matching tempest's class names), add padding to code blocks, and commit
the missing compressed winter.js assets from the earlier asset rename.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

public/assets/highlight/nord.css

@@ -0,0 +1,87 @@
+pre, code {
+    color: #d8dee9;
+    background-color: #2e3440;
+}
+
+.hl-keyword {
+    color: #81A1C1;
+}
+
+.hl-property {
+    color: #88C0D0;
+}
+
+.hl-attribute {
+    font-style: italic;
+}
+
+.hl-type {
+    color: #8FBCBB;
+}
+
+.hl-generic {
+    color: #81A1C1;
+}
+
+.hl-value {
+    color: #A3BE8C;
+}
+
+.hl-literal {
+    color: #A3BE8C;
+}
+
+.hl-number {
+    color: #B48EAD;
+}
+
+.hl-variable {
+    color: #D8DEE9;
+}
+
+.hl-comment {
+    color: #616E88;
+}
+
+.hl-blur {
+    filter: blur(2px);
+}
+
+.hl-strong {
+    font-weight: bold;
+}
+
+.hl-em {
+    font-style: italic;
+}
+
+.hl-addition {
+    display: inline-block;
+    min-width: 100%;
+    background-color: #00FF0022;
+}
+
+.hl-deletion {
+    display: inline-block;
+    min-width: 100%;
+    background-color: #FF000011;
+}
+
+.hl-gutter {
+    display: inline-block;
+    font-size: 0.9em;
+    color: #555;
+    padding: 0 1ch;
+    margin-right: 1ch;
+    user-select: none;
+}
+
+.hl-gutter-addition {
+    background-color: #34A853;
+    color: #fff;
+}
+
+.hl-gutter-deletion {
+    background-color: #EA4334;
+    color: #fff;
+}