style(ext/popup): add color tokens, focus ring, required-pill class

Establishes :root CSS custom properties (accent, surfaces, status, focus
ring) and applies the focus ring to inputs/buttons via :focus-visible.
Adds .req-pill class used by Task 4 to replace the bare-asterisk required
marker. Existing .label .req kept for backward compatibility during the
migration window.

Plan 2026-04-30 fullscreen UX phase 1 task 2.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

extension/src/popup/styles.css

@@ -1,5 +1,31 @@
 /* relicario extension — terminal dark theme */
 
+:root {
+  /* Brand */
+  --accent:        #d2ab43;
+  --accent-soft:   rgba(210, 171, 67, 0.18);
+  --accent-strong: #aa812a;
+
+  /* Surfaces */
+  --bg-page:       #0d1117;
+  --bg-pane:       #161b22;
+  --bg-elevated:   #21262d;
+  --border-subtle: #30363d;
+
+  /* Text */
+  --text:          #c9d1d9;
+  --text-muted:    #8b949e;
+  --text-dim:      #484f58;
+
+  /* Status */
+  --danger:        #ab2b20;
+  --danger-bg:     #791111;
+  --success:       #6cb37a;
+
+  /* Focus */
+  --focus-ring:    0 0 0 2px rgba(210, 171, 67, 0.35);
+}
+
 * {
   margin: 0;
   padding: 0;
@@ -56,11 +82,25 @@ body {
 }
 
 .label .req {
-  color: #aa812a;
+  color: var(--accent-strong);
   margin-left: 2px;
   font-weight: 600;
 }
 
+.req-pill {
+  display: inline-block;
+  font-size: 9px;
+  padding: 1px 5px;
+  background: var(--accent-soft);
+  color: var(--accent);
+  border-radius: 2px;
+  margin-left: 6px;
+  vertical-align: middle;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  font-weight: 500;
+}
+
 .secondary {
   color: #8b949e;
 }
@@ -94,9 +134,9 @@ body {
   background: #30363d;
 }
 
-.btn:focus {
-  outline: 1px solid #d2ab43;
-  outline-offset: 1px;
+.btn:focus-visible {
+  outline: none;
+  box-shadow: var(--focus-ring);
 }
 
 .btn-primary {
@@ -133,8 +173,10 @@ input, textarea, select {
   transition: border-color 0.15s;
 }
 
-input:focus, textarea:focus, select:focus {
-  border-color: #d2ab43;
+input:focus-visible, textarea:focus-visible, select:focus-visible {
+  border-color: var(--accent);
+  box-shadow: var(--focus-ring);
+  outline: none;
 }
 
 input::placeholder, textarea::placeholder {