fix(badges): complete full-chain badge circuit and preset icons

Close the full circuit break in the badge/medal system and replace
empty default icons with preset SVG assets so badges render out of
the box:

- Add aksrt_get_worn_medal_icon() helper that renders the worn medal
  image inline (with settings fallback when the Badges class is
  unavailable).
- Profile header (UC) now shows the worn medal icon beside the name,
  matching zibll's name row order (display_name → VIP → Medal → Level → Verify).
- Add .medal-icon / .aksrt-identity-medal vertical-align rules in UC shell.css.
- Extract SchemaUsers::default_medal_args() and preset 6 badges (rookie,
  checkin-30, writer, popular, annual-star, vip-member) with real icon
  URLs from assets/img/medal/ (medal-1/2/5/9/12/15.svg).
- Vue badge.js: add MEDAL_BASE helper + preset icons matching PHP defaults.

assets/css/routes/user-center/shell.css

@@ -25,6 +25,20 @@
   padding: 0 0 40px;
 }
 
+/* Medal icon alignment in UC header h1 name row (zibll parity). */
+.uc-header__name .medal-icon.img-icon,
+.uc-header__name .aksrt-identity-medal,
+h1.uc-header__name .medal-icon.img-icon,
+h1.uc-header__name .aksrt-identity-medal {
+  width: auto;
+  height: 1.2em;
+  max-width: 6em;
+  object-fit: contain;
+  vertical-align: middle;
+  margin-left: 4px;
+  display: inline-block;
+}
+
 /* ==================== 页面自有双栏（对齐 zibll .user-center flex，不走全站 float 壳） ==================== */
 /* DOM: sidebar first + content second（与 zibll user-center-sidebar / user-center-content 一致）。
  * 选择器同时覆盖 body.aksrt-user-center 与 main.user-center / .aksrt-profile，避免 body class 漏打时失效。 */