fix(gui-v2): SidebarNav uses RouterLink (a11y) + review-nit cleanup

- FIX 1: Replace <button @click="router.push"> with <RouterLink custom>
  + <a> for real link semantics (middle-click, ⌘-click, screen-reader);
  custom isNavItemActive prefix-match stays the active source of truth;
  adds :aria-current="page" on active items; drops useRouter/router.push.
  RouterLink to prop cast via itemTo() helper (RouteLocationRaw from
  unplugin-vue-router) to satisfy typed RouterLinkTyped<RouteNamedMap>.
- FIX 2: Align .nav-item comment to actual template values (py-[9px]
  rounded-md, not CSS vars); replace inaccurate Tailwind v3/v4 before:
  composability justification in <style scoped> with the real reason
  (accent bar at left:-10px is clipped by the overflow-y-auto nav).
- FIX 3: text-left → text-start (logical property, RTL-safe).
- FIX 4: Document id=route-name assumption in useV2Nav.ts with a
  one-line comment at the id: assignment.
- FIX 5: Reword misleading "dotted names" spec description to state
  the real invariant (id = v1 route name, already kebab-case).
- FIX 6: Add 2 tests — useV2Nav wrapper .value equality, and
  consecutive-headings edge case (empty-items group produced).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/app/src/composables/useV2Nav.ts

@@ -55,7 +55,7 @@ export function toV2NavGroups(items: readonly V1NavEntry[]): V2NavGroup[] {
         current = { label: '', items: [] }
 
       const navItem: V2NavItem = {
-        id: entry.to.name,
+        id: entry.to.name, // v1 route names are already kebab-case; no normalisation needed
         label: entry.title,
         icon: entry.icon.icon,
         to: { name: entry.to.name },