style(ui): add color-coded accents and tags to shortcut cards

Introduce per-card accent colors to enhance the visual hierarchy of the documentation shortcut cards. This includes adding left borders, colored eyebrows, and matching hover glows using CSS variables.

Additionally, this commit:
- Adds color-coded tags (GET, POST, JSON, etc.) for API links.
- Implements retro-themed styling for both the shortcut cards and tags to maintain consistency with the classic 16-color VGA palette.
- Applies the new accent classes to the API page template.

backend/static/css/16-retro.css

@@ -801,26 +801,81 @@
   margin-top: 0.5rem;
 }
 
-/* Section intros sit on the black desktop: gold kicker, white title, light
-   subtitle, and readable inline code (not the default black-on-black). */
-:root[data-theme="retro"] .panel-head .kicker {
-  color: #ffd966;
-  display: block;
+/* Section intro becomes a real Win98 window: silver body, the <h2> a navy
+   title bar with a fake close button, and the subtitle as black body text.
+   This fixes the default black-on-black inline code in headings/intros. */
+:root[data-theme="retro"] .panel-head {
+  max-width: none;
+  margin-bottom: 1.5rem;
+  padding: 1rem;
+  background: linear-gradient(to bottom, #ffffff, 4%, #c0c0c0 8%);
+  background-color: #c0c0c0;
+  border: 1px solid #000000;
+  box-shadow: var(--shadow);
 }
 
-:root[data-theme="retro"] .panel-head h2,
+/* The kicker is redundant once the title sits in a title bar; hide it so the
+   bar can hug the top edge (the markup puts the kicker before the h2). */
+:root[data-theme="retro"] .panel-head .kicker {
+  display: none;
+}
+
+:root[data-theme="retro"] .panel-head h2 {
+  position: relative;
+  margin: -1rem -1rem 1rem;
+  padding: 0.35rem 1.8rem 0.35rem 0.5rem;
+  background: linear-gradient(to right, #000078, 80%, #0f80cd);
+  color: #ffffff;
+  font-size: 1rem;
+  font-weight: 700;
+}
+
+/* Inline code in the title (e.g. "The warpbox CLI") reads white on the bar
+   instead of the default black. */
+:root[data-theme="retro"] .panel-head h2 code {
+  color: #ffffff;
+  background: transparent;
+  padding: 0;
+}
+
+:root[data-theme="retro"] .panel-head h2::after {
+  content: "\2715";
+  position: absolute;
+  top: 50%;
+  right: 0.4rem;
+  transform: translateY(-50%);
+  display: grid;
+  place-items: center;
+  width: 1.15rem;
+  height: 1rem;
+  background: #c0c0c0;
+  color: #000000;
+  font-size: 0.7rem;
+  font-weight: 700;
+  box-shadow: inset -1px -1px 0 #404040, inset 1px 1px 0 #ffffff, inset -2px -2px 0 #808080, inset 2px 2px 0 #dfdfdf;
+}
+
+:root[data-theme="retro"] .panel-head .lead {
+  color: #1a1a1a;
+  margin: 0;
+}
+
+/* Inline code in the subtitle: sunken white field, black text. */
+:root[data-theme="retro"] .panel-head .lead code {
+  color: #000000;
+  background: #ffffff;
+  border: 1px solid #808080;
+  padding: 0 0.2rem;
+}
+
+/* The lone "Quick links" label on the home desktop stays light. */
 :root[data-theme="retro"] .section-label {
   color: #ffffff;
 }
 
-:root[data-theme="retro"] .panel-head .lead {
-  color: #cfd8ff;
-}
-
-:root[data-theme="retro"] .panel-head .lead code {
-  color: #ffffff;
-  background: #000078;
-  padding: 0 0.2rem;
+/* ShareX step lists are light-muted by default; black on the silver window. */
+:root[data-theme="retro"] .docs-steps {
+  color: #1a1a1a;
 }
 
 /* Each card heading becomes a Win98 title bar with a fake close button.
@@ -903,6 +958,7 @@
 :root[data-theme="retro"] .shortcut-card:hover {
   transform: none;
   background-color: #d4d0c8;
+  box-shadow: inset -1px -1px 0 #404040, inset 1px 1px 0 #ffffff, inset -2px -2px 0 #808080, inset 2px 2px 0 #dfdfdf;
 }
 
 :root[data-theme="retro"] .shortcut-eyebrow {
@@ -927,6 +983,14 @@
   border: 1px solid #000000;
 }
 
+/* Colour-coded badges in the classic 16-colour VGA palette, with black
+   borders so they read like little Win98 toolbar icons. */
+:root[data-theme="retro"] .link-pill .tag-get { background: #0000aa; color: #ffffff; }
+:root[data-theme="retro"] .link-pill .tag-post { background: #008000; color: #ffffff; }
+:root[data-theme="retro"] .link-pill .tag-json { background: #aa00aa; color: #ffffff; }
+:root[data-theme="retro"] .link-pill .tag-key { background: #aa5500; color: #ffffff; }
+:root[data-theme="retro"] .link-pill .tag-help { background: #00aaaa; color: #000000; }
+
 /* CLI download cards = silver windows. */
 :root[data-theme="retro"] .download-card {
   background: linear-gradient(to bottom, #ffffff, 4%, #c0c0c0 8%);