clean exemple/navigation to a minimal working example

- index.html: fix title and typo, add missing #error div
- config.json: replace project-specific keys with generic api_url
- core/menu.js: remove Voltalis mock data, leave commented usage pattern
- dashboard.js: move logic to init(), Custom Element is a plain shell
- dashboard.css: add real styles, remove placeholder comment
- manifest.json: drop unused version field
- config.yml: fix web/vendor comment → sources/vendor

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: GnomeZworc <nicolas.boufidjeline@g3e.fr>

exemple/navigation/sources/pages/dashboard/manifest.json

@@ -1,6 +1,5 @@
 {
-  "route":   "dashboard",
-  "label":   "Dashboard",
-  "icon":    "dashboard",
-  "version": "0.1.0"
+  "route": "dashboard",
+  "label": "Dashboard",
+  "icon":  "dashboard"
 }