site-builder: feedback batch (social, features, header menu, spacer)

Five of six items from user feedback (Contact Form email delivery split
into a focused, live-tested follow-up):

- Social Links: add Spotify + Twitch (FA 4.7.0 already ships both glyphs).
- Features Grid: per-feature icon/image toggle (upload + URL) and an
  optional button (text + url); render, settings, and HTML export updated,
  backward compatible with existing icon-only features.
- Header: seed the default header with a Navbar (logo + Home/About/Services/
  Contact) so new sites open with an editable menu-with-links instead of an
  empty header zone. Adds a vitest guard that the seed deserializes and
  exports a real <nav>.
- Canvas: slim the empty header/footer placeholder from a padded band to a
  thin hint line so an empty zone no longer reads as a stray spacer.

Design spec: docs/superpowers/specs/2026-07-06-site-builder-feedback-batch-design.md

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/state/PageContext.tsx

@@ -60,6 +60,60 @@ const EMPTY_HEADER =
 const EMPTY_FOOTER =
   '{"ROOT":{"type":{"resolvedName":"Container"},"isCanvas":true,"props":{"style":{"minHeight":"60px","backgroundColor":"#0f172a","color":"#94a3b8","padding":"40px 24px","textAlign":"center"},"tag":"footer"},"displayName":"Container","custom":{},"hidden":false,"nodes":[],"linkedNodes":{}}}';
 
+// Default header seed: a ROOT header Container holding a Navbar with default
+// links. New sites previously opened with an EMPTY header (just a bare
+// Container), so there was no menu to edit and the empty zone rendered as a
+// stray band above the page. Seeding a real Navbar gives every new site an
+// editable menu-with-links out of the box (and removes the empty-header gap).
+// Node shape matches serializeTreeForCraft() / Craft's actions.deserialize().
+export const DEFAULT_HEADER_STATE = JSON.stringify({
+  ROOT: {
+    type: { resolvedName: 'Container' },
+    isCanvas: true,
+    props: { style: { width: '100%' }, tag: 'header' },
+    displayName: 'Container',
+    custom: {},
+    hidden: false,
+    nodes: ['header-navbar'],
+    linkedNodes: {},
+  },
+  'header-navbar': {
+    type: { resolvedName: 'Navbar' },
+    isCanvas: false,
+    props: {
+      logoType: 'text',
+      logoText: 'MySite',
+      logoImage: '',
+      logoWidth: '120px',
+      logoUrl: '/',
+      logoFontFamily: 'Inter, sans-serif',
+      logoFontSize: '20px',
+      links: [
+        { text: 'Home', href: '/' },
+        { text: 'About', href: '#about' },
+        { text: 'Services', href: '#services' },
+        { text: 'Contact', href: '#contact', isCta: true },
+      ],
+      backgroundColor: '#ffffff',
+      textColor: '#3f3f46',
+      hoverColor: '#3b82f6',
+      ctaColor: '#3b82f6',
+      ctaTextColor: '#ffffff',
+      padding: '16px 24px',
+      navAlignment: 'space-between',
+      isSticky: false,
+      showMobileMenu: false,
+      style: { borderBottom: '1px solid #e4e4e7' },
+    },
+    displayName: 'Navbar',
+    parent: 'ROOT',
+    custom: {},
+    hidden: false,
+    nodes: [],
+    linkedNodes: {},
+  },
+});
+
 const PageContext = createContext<PageContextValue>({
   pages: [],
   headerPage: { id: HEADER_ID, name: 'Header', slug: '__header__', craftState: null, headCode: '' },
@@ -106,7 +160,7 @@ const DEFAULT_HEADER: PageData = {
   id: HEADER_ID,
   name: 'Header',
   slug: '__header__',
-  craftState: null,
+  craftState: DEFAULT_HEADER_STATE,
   headCode: '',
 };