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/core/menu.js

@@ -1,37 +1,10 @@
-// Dynamic menu loader.
-// Fetches data for groups declared with empty children in navigation.json
-// and injects them into side-nav after it is ready.
-//
+// Dynamic menu loader — injects children into named groups in the side-nav.
 // Imported non-blocking from index.html — does not delay routing.
-// Replace MOCK_* with real api-client calls when the backend is ready.
-
-// ── Mock data ────────────────────────────────────────────────────────────────
-
-const MOCK_ACCOUNTS = [
-  { id: 'tresorerie',   name: 'Trésorerie'   },
-  { id: 'charges',      name: 'Charges'       },
-  { id: 'produits',     name: 'Produits'      },
-  { id: 'fournisseurs', name: 'Fournisseurs'  },
-]
-
-async function fetchAccounts() {
-  // TODO: replace with real call
-  // const api = document.querySelector('api-client')
-  // return await api.finance.list('/accounts')
-  await new Promise(r => setTimeout(r, 500))  // simulate network latency
-  return MOCK_ACCOUNTS
-}
-
-// ── Injection ────────────────────────────────────────────────────────────────
-
-const nav = document.querySelector('side-nav')
-if (!nav) throw new Error('menu.js: side-nav not found in DOM')
-
-await nav.ready
-
-const accounts = await fetchAccounts()
-nav.setGroupChildren('Comptes', accounts.map(a => ({
-  label: a.name,
-  href:  `#/account?id=${a.id}`,
-  icon:  'account',
-})))
+//
+// Example: populate a group declared in config.yml.
+//
+//   const nav = document.querySelector('side-nav')
+//   await nav.ready
+//   nav.setGroupChildren('Mon Groupe', [
+//     { label: 'Item A', href: '#/item-a', icon: 'folder' },
+//   ])