chore: resolve dev dependency audit findings (WealthLedger/docs#55)

Bump markdownlint-rule-relative-links to 5.1.4 and pin markdown-it to
15.0.3 via overrides (fixes high-severity advisory). Also resolves the
moderate ip-address advisory. npm audit --include=dev reports 0.

package.json

@@ -18,7 +18,7 @@
     "@release-it/conventional-changelog": "12.0.0",
     "conventional-changelog-conventionalcommits": "10.4.0",
     "markdownlint-cli": "0.49.1",
-    "markdownlint-rule-relative-links": "5.1.3",
+    "markdownlint-rule-relative-links": "5.1.4",
     "release-it": "21.0.2"
   },
   "overrides": {
@@ -30,6 +30,7 @@
     "release-it": {
       "basic-ftp": "6.2.1",
       "undici": "7.29.1"
-    }
+    },
+    "markdown-it": "15.0.3"
   }
 }