feat(web): add i18n support with FR/EN locales and keyboard layout awareness

Add full internationalization system with React context, French/English
translations, and AZERTY/QWERTY keyboard layout support. Dashboard now
uses a tabbed layout (Tools, Notifications, Workflows). Config page exposes
language and keyboard preferences persisted via new /api/preferences endpoint.

💕 Generated with Crush

Assisted-by: GLM-5-Turbo via Crush <crush@charm.land>

web/src/api/client.js

@@ -25,6 +25,7 @@ const api = {
   runScan: () => request('/scan', { method: 'POST' }),
   installTools: (tools) => request('/install', { method: 'POST', body: JSON.stringify({ tools }) }),
   configureMCP: () => request('/mcp/configure', { method: 'POST' }),
+  savePreferences: (prefs) => request('/preferences', { method: 'PUT', body: JSON.stringify(prefs) }),
   runCommand: (command, cwd) => request('/terminal', { method: 'POST', body: JSON.stringify({ command, cwd }) }),
 }