chore: bump vue from 2.6.11 to 2.7.16

[anthonyshchang]

🔧 Bump vue to 2.7.16
This PR bumps the Vue-related dependencies to 2.7.16 to resolve a version mismatch introduced while addressing a security alert.

🛠 Context

• While bumping elliptic from 6.5.4 → 6.6.1 (per Dependabot), the build began failing due to a missing vuepress dependency.
• Installing vuepress@1.9.x (or even 1.8.2) introduces vue-server-renderer@2.7.16, which mismatches with our existing vue@2.6.11 and causes build errors:

Error: Vue packages version mismatch:
- vue@2.6.11
- vue-server-renderer@2.7.16