Upgrade vue-router 4.3.0 → 5.2.0

[n-lark]

Upgrade vue-router 4.3.0 → 5.2.0 (major)

Dependabot PR #7857. Runtime dependency (dependencies, ^4.2.5); the app router — createRouter in frontend/src/routes.js, plus useRouter/useRoute across frontend/src/. Pulled out of the weekly Dependabot slot per the major-version process — needs an owner and verification, not a batch merge.

Compatibility pre-check

• Vue peer ^3.5.34 || ^4.0.0 vs installed vue@3.5.38 — ✅
• Extra peers (vite ^7.3.0 || ^8.0.0, pinia, @pinia/colada, @vue/compiler-sfc) are all optional: true — for the merged file-based/typed-routes tooling we don't use; installed vite@6.4.2 / pinia@3.0.4 unaffected — ✅
• No engines field on vue-router@5.2.0 — ✅

Breaking changes to review

• v4→v5 is a "boring" release merging unplugin-vue-router into core; migration guide states no breaking changes for non-file-based users (source: v4-to-v5 migration guide).
• IIFE build no longer bundles @vue/devtools-api (v8) — only affects the standalone browser build, not bundled apps.
• 5.0.3: next()-callback guards emit deprecation warnings; NavigationResult deprecated in favor of reroute(to) (experimental APIs) — to confirm from changelog.

To do before merge

• Verify routing/navigation still works — createRouter + createWebHistory in frontend/src/routes.js.
• Check next()-callback guards for new deprecation warnings: beforeEach in routes.js, and beforeEnter guards ensurePermission.ts / ensureAdmin.ts.
• Confirm lazy/dynamic route imports still resolve.
• Read the 5.x changelog / migration notes and reconcile with our usage.

Refs

• Branch: dependabot/npm_and_yarn/vue-router-5.2.0
• PR: build(deps): bump vue-router from 4.3.0 to 5.2.0 #7857
• Upstream: https://github.com/vuejs/router/releases and https://router.vuejs.org/guide/migration/v4-to-v5.html