feat: add custom CSS save system with dual-editor interface

Implement complete custom CSS management system:
- Separate base CSS (readonly) and custom CSS (editable)
- Save custom CSS to Kirby backend per narrative
- Visual save button with state indicators (dirty/saving/success/error)
- CSRF-protected API endpoint for CSS operations
- Dual-editor StylesheetViewer (base + custom with edit mode toggle)
- Auto-format custom CSS with Prettier on edit mode exit

Backend changes:
- Add web2print Kirby plugin with POST/GET routes
- Add customCss field to narrative blueprint
- Add CSRF token meta tag in header
- Include customCss and modified timestamps in JSON template
- Install code-editor plugin for Kirby panel

Frontend changes:
- Refactor stylesheet store with baseCss/customCss refs
- Make content a computed property (baseCss + customCss)
- Add helper methods: replaceBlock, replaceInCustomCss, setCustomCss
- Update all components to use new store API
- Create SaveButton component with FAB design
- Redesign StylesheetViewer with collapsable sections
- Initialize store from narrative data on app mount

File changes:
- Rename stylesheet.css → stylesheet.print.css
- Update all references to new filename

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

public/site/plugins/code-editor/eslint.config.mjs

@@ -0,0 +1,28 @@
+import js from "@eslint/js";
+import prettier from "eslint-config-prettier";
+import vue from "eslint-plugin-vue";
+
+export default [
+	js.configs.recommended,
+	...vue.configs["flat/vue2-recommended"],
+	prettier,
+	{
+		rules: {
+			"vue/attributes-order": "error",
+			"vue/component-definition-name-casing": "off",
+			"vue/html-closing-bracket-newline": [
+				"error",
+				{
+					singleline: "never",
+					multiline: "always"
+				}
+			],
+			"vue/multi-word-component-names": "off",
+			"vue/require-default-prop": "off",
+			"vue/require-prop-types": "error"
+		},
+		languageOptions: {
+			ecmaVersion: 2022
+		}
+	}
+];