Give the homepage teaser a rich text editor

Replace the plain textarea for the homepage_teaser setting with the shared
TipTap rich-text editor, and render the teaser as sanitized HTML in the
portal hero's default layout.

- SettingsAdmin: teaser field now uses RichTextEditor (lazy-loaded, code-split
  like PostEditor); rich fields render in a <div> wrapper instead of <label>.
- HeroElement: text-block lines flagged `html` render sanitized HTML.
- heroLayout: the default-layout teaser line is now an HTML line.
- admin.controller: sanitize homepage_teaser against the body allowlist on save.
- theme.css: collapse the teaser's nested block margins in the hero.

Closes #48

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/routes/admin/views/SettingsAdmin.jsx

@@ -1,13 +1,21 @@
-import { useEffect, useState } from 'react'
+import { lazy, Suspense, useEffect, useState } from 'react'
 import { Loading, ErrorState } from '../../../components/PageState.jsx'
 import { api } from '../../../api/client.js'
 import { useSite } from '../../../contexts/SiteContext.jsx'
 import EmailDelivery from './EmailDelivery.jsx'
 
+// Lazy-loaded so the heavy rich-text editor stays code-split (matches PostEditor).
+const RichTextEditor = lazy(() => import('../../../components/RichTextEditor.jsx'))
+
 // Editable settings shown on this screen (key -> label + control type).
 const FIELDS = [
   { key: 'site_title', label: 'Site title' },
-  { key: 'homepage_teaser', label: 'Homepage teaser', long: true },
+  {
+    key: 'homepage_teaser',
+    label: 'Homepage teaser',
+    rich: true,
+    help: 'Rich text shown under the hero heading on the portal (when no custom hero layout is published).',
+  },
   { key: 'maintenance_message', label: 'Maintenance message', long: true },
   { key: 'status_message', label: 'Status message' },
   {
@@ -59,10 +67,13 @@ export default function SettingsAdmin() {
   if (loading) return <Loading />
   if (error) return <ErrorState message={error} />
 
-  const set = (k) => (e) => {
-    setValues((v) => ({ ...v, [k]: e.target.value }))
+  // setRaw takes the next value directly (rich editor onChange), set adapts a
+  // DOM change event onto it.
+  const setRaw = (k) => (val) => {
+    setValues((v) => ({ ...v, [k]: val }))
     setSaved(false)
   }
+  const set = (k) => (e) => setRaw(k)(e.target.value)
 
   async function save() {
     setBusy(true)
@@ -82,10 +93,18 @@ export default function SettingsAdmin() {
   return (
     <section style={{ maxWidth: 620 }}>
       <div style={{ display: 'flex', flexDirection: 'column', gap: 18 }}>
-        {FIELDS.map((f) => (
-          <label key={f.key} style={{ display: 'block' }}>
+        {FIELDS.map((f) => {
+          // A rich field can't live inside a <label> (nested toolbar buttons +
+          // contenteditable), so it uses a plain <div> wrapper instead.
+          const Wrap = f.rich ? 'div' : 'label'
+          return (
+          <Wrap key={f.key} style={{ display: 'block' }}>
             <span className="field-label">{f.label}</span>
-            {f.options ? (
+            {f.rich ? (
+              <Suspense fallback={<span className="spin" />}>
+                <RichTextEditor value={values[f.key]} onChange={setRaw(f.key)} variant="post" />
+              </Suspense>
+            ) : f.options ? (
               <select value={values[f.key]} onChange={set(f.key)} className="select">
                 {f.options.map((o) => (
                   <option key={o.value} value={o.value}>
@@ -103,8 +122,9 @@ export default function SettingsAdmin() {
                 {f.help}
               </span>
             )}
-          </label>
-        ))}
+          </Wrap>
+          )
+        })}
         <div style={{ display: 'flex', gap: 10, marginTop: 6, alignItems: 'center' }}>
           <button onClick={save} disabled={busy} className="btn btn-primary btn-sq">
             {busy ? 'Saving…' : 'Save changes'}