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/src/node/patchVuePrismEditor.mjs

@@ -0,0 +1,38 @@
+import { existsSync, readFileSync, writeFileSync } from "fs";
+import chalk from "chalk";
+import consola from "consola";
+
+const srcPath = "node_modules/vue-prism-editor/dist/prismeditor.esm.js";
+
+async function main() {
+  consola.start("Vue Prism Editor patcher");
+
+  if (!existsSync(srcPath)) {
+    consola.error(
+      `couldn't find ${chalk.cyan(srcPath)}, did you run ${chalk.green(
+        "npm install"
+      )}?`
+    );
+    return;
+  }
+
+  const source = readFileSync(srcPath, "utf8");
+
+  if (!source.includes("Vue.extend")) {
+    consola.success("already patched");
+    return;
+  }
+
+  consola.info("patching the source component...");
+
+  let output = source
+    .replace(/^import Vue from 'vue';/, "")
+    .replace("/*#__PURE__*/Vue.extend(", "")
+    .replace(/\}\)(;\s+export)/, "}$1");
+
+  writeFileSync(srcPath, output, "utf8");
+
+  consola.success("successfully patched");
+}
+
+main().catch((err) => consola.error(err));