feat(ext/icons): replace idfoto ID-card icon with reliquary design

The prior icon was a holdover from the pre-rename idfoto project — a
stylized ID card with a portrait silhouette. Replaced with a proper
reliquary: an arched vessel with a horizontal seal band, small rivets,
standing on a blue pedestal, with a faceted gem at center representing
the protected relic.

- relicario-logo.svg: full 128-px-native design used by the setup
  wizard header and rasterized to icon-48.png and icon-128.png.
- relicario-logo-16.svg: 16-px-optimized variant (bolder strokes, no
  rivets, single-facet gem) for crisp toolbar rendering.
- Palette matches the gh-dark aesthetic used across the extension
  (#0d1117 / #161b22 background, #58a6ff / #79c0ff / #1f6feb accents).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

extension/icons/relicario-logo-16.svg

@@ -0,0 +1,24 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" fill="none">
+  <!-- 16x16-optimized: bolder strokes, simplified details, single gem
+       facet for crisp pixels at toolbar size. -->
+
+  <!-- Base plate -->
+  <rect x="1" y="13" width="14" height="2" rx="0.5" fill="#58a6ff"/>
+
+  <!-- Arched reliquary body -->
+  <path d="M 3 13
+           L 3 6
+           C 3 3.5, 5 2, 8 2
+           C 11 2, 13 3.5, 13 6
+           L 13 13 Z"
+        fill="#161b22"
+        stroke="#58a6ff"
+        stroke-width="1"
+        stroke-linejoin="round"/>
+
+  <!-- Seal band -->
+  <rect x="3" y="6" width="10" height="1" fill="#58a6ff"/>
+
+  <!-- Central gem — a simple filled diamond -->
+  <path d="M 8 8 L 10 10 L 8 12 L 6 10 Z" fill="#58a6ff"/>
+</svg>