feat: Add theme system with visual editor

- Backend: themes table and API endpoints (CRUD, export, design-tokens)
- Theme store with preview, apply, and persistence
- ThemesPage with collapsible variables editor and live preview
- Components: ColorPicker (HSL), VariableEditor, ThemePreview, ThemeListItem
- Integration: $theme helper for dynamic components, get_design_tokens MCP tool
- Navigation: /themes route with palette icon in toolbar

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/package-lock.json

@@ -11,7 +11,8 @@
         "@nucleoriofrio/webmcp": "git+https://gitea.nucleoriofrio.com/nucleo000/webmcp.git",
         "pinia": "^3.0.4",
         "vite-plugin-pwa": "^1.2.0",
-        "vue": "^3.5.25"
+        "vue": "^3.5.25",
+        "vue-router": "^4.6.4"
       },
       "devDependencies": {
         "@types/node": "^24.10.1",
@@ -5330,6 +5331,27 @@
         }
       }
     },
+    "node_modules/vue-router": {
+      "version": "4.6.4",
+      "resolved": "https://registry.npmjs.org/vue-router/-/vue-router-4.6.4.tgz",
+      "integrity": "sha512-Hz9q5sa33Yhduglwz6g9skT8OBPii+4bFn88w6J+J4MfEo4KRRpmiNG/hHHkdbRFlLBOqxN8y8gf2Fb0MTUgVg==",
+      "license": "MIT",
+      "dependencies": {
+        "@vue/devtools-api": "^6.6.4"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/posva"
+      },
+      "peerDependencies": {
+        "vue": "^3.5.0"
+      }
+    },
+    "node_modules/vue-router/node_modules/@vue/devtools-api": {
+      "version": "6.6.4",
+      "resolved": "https://registry.npmjs.org/@vue/devtools-api/-/devtools-api-6.6.4.tgz",
+      "integrity": "sha512-sGhTPMuXqZ1rVOk32RylztWkfXTRhuS7vgAKv0zjqk8gbsHkJ7xfFf+jbySxt7tWObEJwyKaHMikV/WGDiQm8g==",
+      "license": "MIT"
+    },
     "node_modules/vue-tsc": {
       "version": "3.2.4",
       "dev": true,