feat: add config page with LLM settings and tag management

Add ConfigPage.vue with two sections: Ollama configuration (URL, model,
timeout) with source badges and per-field reset, and tag management with
inline rename and creation. Add /config route and nav link.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/router.js

@@ -6,6 +6,7 @@ import RevenusPage from './pages/RevenusPage.vue'
 import DocumentsPage from './pages/DocumentsPage.vue'
 import EditDocumentPage from './pages/EditDocumentPage.vue'
 import IAPage from './pages/IAPage.vue'
+import ConfigPage from './pages/ConfigPage.vue'
 
 const routes = [
   {
@@ -33,6 +34,11 @@ const routes = [
     name: 'ia',
     component: IAPage
   },
+  {
+    path: '/config',
+    name: 'config',
+    component: ConfigPage
+  },
   {
     path: '/documents',
     name: 'documents',