fix(cms): enable the Tailwind typography plugin so prose classes work (#1288)

tailwind.config.js had plugins: [] and @tailwindcss/typography was never
installed, so every prose / prose-neutral / dark:prose-invert class in the
app resolved to nothing. Preflight, which IS active, resets h1-h6 to
inherit size and weight and strips list-style from ul/ol — so an applied
<h2> rendered pixel-identical to the <p> it replaced.

The editor was never broken. The toolbar highlighted because
editor.isActive('heading') correctly returned true; only the CSS to show
it was missing. That also explains why pasting rendered rich text worked:
it carries inline styles.

Ten surfaces rely on these classes, including the PUBLIC CMS pages — so
impressum/datenschutz were serving unstyled headings to visitors too.

Review follow-ups: prose colours are mapped to the theme tokens wherever
.text-theme marks theme-owned text (a dark gallery preset sets
--color-text but no .dark class, so dark:prose-invert never engages and
headings would have gone near-black on dark); code blocks inherit rather
than being scaled twice; and H5/H6 get explicit rules, since the plugin
only styles h1-h4.

Closes #1288

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "picpeak-frontend",
-  "version": "3.122.5-beta.0",
+  "version": "3.122.6-beta.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "picpeak-frontend",
-      "version": "3.122.5-beta.0",
+      "version": "3.122.6-beta.0",
       "dependencies": {
         "@dagrejs/dagre": "^3.0.0",
         "@fullcalendar/core": "^6.1.20",
@@ -59,6 +59,7 @@
       },
       "devDependencies": {
         "@eslint/js": "^9.29.0",
+        "@tailwindcss/typography": "^0.5.20",
         "@testing-library/jest-dom": "^6.6.3",
         "@testing-library/react": "^16.1.0",
         "@testing-library/user-event": "^14.6.1",
@@ -2843,6 +2844,33 @@
         "@swc/counter": "^0.1.3"
       }
     },
+    "node_modules/@tailwindcss/typography": {
+      "version": "0.5.20",
+      "resolved": "https://registry.npmjs.org/@tailwindcss/typography/-/typography-0.5.20.tgz",
+      "integrity": "sha512-hwbzQuNUfcPvbegQFatVPl/MY/tcM9KLl963hQ5laJKPh81TEZ1+dNG9PirGvcaDBkp+BCshExAyKVPW91dozw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "postcss-selector-parser": "6.0.10"
+      },
+      "peerDependencies": {
+        "tailwindcss": ">=3.0.0 || >=4.0.0 || insiders"
+      }
+    },
+    "node_modules/@tailwindcss/typography/node_modules/postcss-selector-parser": {
+      "version": "6.0.10",
+      "resolved": "https://registry.npmjs.org/postcss-selector-parser/-/postcss-selector-parser-6.0.10.tgz",
+      "integrity": "sha512-IQ7TZdoaqbT+LCpShg46jnZVlhWD2w6iQYAcYXfHARZ7X1t/UGhhceQDs5X0cGqKvYlHNOuv7Oa1xmb0oQuA3w==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "cssesc": "^3.0.0",
+        "util-deprecate": "^1.0.2"
+      },
+      "engines": {
+        "node": ">=4"
+      }
+    },
     "node_modules/@tanstack/query-core": {
       "version": "5.90.16",
       "resolved": "https://registry.npmjs.org/@tanstack/query-core/-/query-core-5.90.16.tgz",
@@ -7592,7 +7620,6 @@
       "integrity": "sha512-QP88BAKvMam/3NxH6vj2o21R6MjxZUAd6nlwAS/pnGvN9IVLocLHxGYIzFhg6fUQ+5th6P4dv4eW9jX3DSIj7A==",
       "dev": true,
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=12"
       },
@@ -8843,6 +8870,7 @@
       "integrity": "sha512-6A2rnmW5xZMdw11LYjhcI5846rt9pbLSabY5XPxo+XWdxwZaFEn47Go4NzFiHu9sNNmr/kXivP1vStfvMaK1GQ==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@alloc/quick-lru": "^5.2.0",
         "arg": "^5.0.2",