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.json

@@ -13,7 +13,8 @@
     "@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",