Add new sections, update design system, fix header mobile layout

Sections:
- Add announcement-bar, cards, features-3col-cards, hero-card-homepage, hero-card-page, hero-slider
- Rename content-image-right → content-image (image-left layout, better mobile stacking)

Design system:
- Add cards-grid global class (flex-wrap for fluid wrapping card grids)
- Update feature-card with responsive _widthMax constraints (33%/50%/95%)
- Document Bricks Style Manager spacing setup in design.md

Headers:
- Fix header-with-cta mobile hamburger positioning — wrap nav+button in block element with row-reverse on mobile

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

headers/header-with-cta.json

@@ -21,7 +21,7 @@
       "id": "con001",
       "name": "container",
       "parent": "sec001",
-      "children": ["log001", "nav001", "btn001"],
+      "children": ["log001", "blk001"],
       "settings": {
         "_direction": "row",
         "_alignItems": "center",
@@ -36,21 +36,51 @@
       "children": [],
       "settings": []
     },
+    {
+      "id": "blk001",
+      "name": "block",
+      "parent": "con001",
+      "children": ["nav001", "btn001"],
+      "settings": {
+        "_direction": "row",
+        "_alignItems": "center",
+        "_justifyContent": "space-around",
+        "_columnGap": "var(--col-gap)",
+        "_rowGap": "var(--row-gap)",
+        "_direction:mobile_portrait": "row-reverse",
+        "_direction:mobile_landscape": "row-reverse",
+        "_width:mobile_landscape": "fit-content",
+        "_columnGap:mobile_landscape": "var(--col-gap)",
+        "_rowGap:mobile_landscape": "var(--row-gap)"
+      },
+      "label": "Nav Group"
+    },
     {
       "id": "nav001",
       "name": "nav-menu",
-      "parent": "con001",
+      "parent": "blk001",
       "children": [],
-      "settings": []
+      "settings": {
+        "subMenuTransform": {
+          "translateY": "28px"
+        },
+        "mobileMenuToggleColor:mobile_portrait": {
+          "raw": "var(--color-white)"
+        },
+        "mobileMenuToggleColor:mobile_landscape": {
+          "raw": "var(--color-white)"
+        }
+      }
     },
     {
       "id": "btn001",
       "name": "button",
-      "parent": "con001",
+      "parent": "blk001",
       "children": [],
       "settings": {
         "text": "Get in Touch",
-        "style": "primary"
+        "style": "primary",
+        "_display:mobile_portrait": "none"
       }
     }
   ]