feat(apps): OBD2 placeholder rail item (launchpad for the parked OBD2 project)

Adds an OBD2 item to the Apps rail; with no records UI deployed yet it links to
the OBD2 Telemetry project + tasks and the research/wiki page rather than
embedding. Swap to embedView once LubeLogger/Tracktor is up. → 2.1.1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/components/sidebar.js

@@ -131,7 +131,8 @@ export function renderSidebar(root) {
     el('div', { class: 'sb-section' },
       el('div', { class: 'sb-title' }, 'Apps'),
       navItem('Timelapse', '/timelapse'),
-      navItem('AI Usage', '/ai-usage')
+      navItem('AI Usage', '/ai-usage'),
+      navItem('OBD2', '/obd2')
     )
   );