fix(ui): address further PR review comments

- Replace custom UNSAFE_HREF_RE with @braintree/sanitize-url for robust XSS prevention
- Shorten renderInlineMarkdown JSDoc
- Single-user with href: collapse two adjacent links into one wrapping avatar + name
- Multi-user list: use href ?? index:name as key to avoid collisions on duplicate names
- Status dot: replace role="img"/aria-label with aria-hidden (text label is sufficient)

Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>

yarn.lock

@@ -7973,6 +7973,7 @@ __metadata:
   dependencies:
     "@backstage/cli": "workspace:^"
     "@backstage/version-bridge": "workspace:^"
+    "@braintree/sanitize-url": "npm:^7.1.2"
     "@remixicon/react": "npm:^4.6.0"
     "@storybook/react-vite": "npm:^10.3.3"
     "@tanstack/react-table": "npm:^8.21.3"
@@ -8046,6 +8047,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@braintree/sanitize-url@npm:^7.1.2":
+  version: 7.1.2
+  resolution: "@braintree/sanitize-url@npm:7.1.2"
+  checksum: 10/d9626ff8f8eb5e192cd055e6e743449c21102c76bb59e405b7028fe56230fa080bfcc80dfb1e21850a6876e75adda9f7b3c888cf0685942bb74da4d2866d6ec3
+  languageName: node
+  linkType: hard
+
 "@bundled-es-modules/cookie@npm:^2.0.1":
   version: 2.0.1
   resolution: "@bundled-es-modules/cookie@npm:2.0.1"