feat(hero): Phase 3 — media slot and split-layout variants

- New `content.media` field accepts image (Hugo-pipeline-processed for
  responsive srcset) or video (passes through as <video>). Optional
  `dark_src` provides a dark-mode image variant.
- New `design.layout` enum: centered (default) | split-left |
  split-right | stacked. Split layouts auto-set alignment to 'left'
  unless explicitly overridden.
- Bump trust-strip star size from w-4 to w-5 for visual presence.
- Two new shared partials in layouts/_partials/functions/:
  - resolve_image_resource: path → {resource | fallback_url}
  - process_image_for_props: path → {src, srcset, width, height}
  These factor out the resource-resolution + responsive-processing
  pipeline so media-bearing blocks don't have to inline it.
- Capabilities registry: media-image, media-video, split-layouts.
- Landing page _index.md: keeps the centered hero (no behavioural
  change) but documents the opt-in pattern for split layouts inline.

modules/blox/layouts/_partials/blox/preact-wrapper.html

@@ -33,6 +33,24 @@
   {{ end }}
 {{ end }}
 
+{{/* Resolve hero media (single image, optional dark variant). Videos pass through unprocessed. */}}
+{{ with $block.content.media }}
+  {{ if or (not .type) (eq .type "image") }}
+    {{ with .src }}
+      {{ $img_data := partial "functions/process_image_for_props" (dict "path" . "Page" $page) }}
+      {{ with $img_data.src }}
+        {{ $props = merge $props (dict "media_image" $img_data) }}
+      {{ end }}
+    {{ end }}
+    {{ with .dark_src }}
+      {{ $img_data := partial "functions/process_image_for_props" (dict "path" . "Page" $page) }}
+      {{ with $img_data.src }}
+        {{ $props = merge $props (dict "media_image_dark" $img_data) }}
+      {{ end }}
+    {{ end }}
+  {{ end }}
+{{ end }}
+
 {{/* Resolve icon for single button (cta-card) */}}
 {{ with $block.content.button.icon }}
   {{ $icon_data := partial "functions/get_icon_data" (dict "name" .) }}

modules/blox/layouts/_partials/functions/process_image_for_props.html

@@ -0,0 +1,45 @@
+{{/*
+  process_image_for_props — One-shot helper: resolves an image path and returns a
+  {src, srcset?, width?, height?} dict ready to merge into a Preact block's props.
+  SVGs and GIFs pass through unprocessed (preserves vectors / animation frames).
+
+  Inputs:
+    .path:  image path (required)
+    .Page:  current page (recommended for page-resource lookup)
+    .sizes: slice of widths for srcset generation
+            (optional, defaults to [600, 900, 1200, 1800])
+
+  Returns: image data dict {src, srcset?, width?, height?}, or empty dict if the
+  path is missing or unresolvable.
+*/}}
+{{ $result := dict }}
+{{ $path := .path | default "" }}
+
+{{ if $path }}
+  {{ $sizes := .sizes | default (slice 600 900 1200 1800) }}
+  {{ $resolved := partial "functions/resolve_image_resource" (dict "path" $path "Page" .Page) }}
+
+  {{ with $resolved.resource }}
+    {{ $canProcess := and (reflect.IsImageResourceProcessable .) (ne .MediaType.SubType "gif") }}
+    {{ if not $canProcess }}
+      {{ $result = dict "src" .RelPermalink }}
+    {{ else }}
+      {{ $responsive := partial "functions/process_responsive_image.html" (dict
+          "image" .
+          "mode" "fit"
+          "sizes" $sizes
+      ) }}
+      {{ $result = dict
+          "src" $responsive.fallback.RelPermalink
+          "srcset" $responsive.srcset
+          "width" $responsive.fallback.Width
+          "height" $responsive.fallback.Height
+      }}
+    {{ end }}
+  {{ end }}
+  {{ with $resolved.fallback_url }}
+    {{ $result = dict "src" . }}
+  {{ end }}
+{{ end }}
+
+{{ return $result }}

modules/blox/layouts/_partials/functions/resolve_image_resource.html

@@ -0,0 +1,54 @@
+{{/*
+  resolve_image_resource — Resolves an image path string to either a Hugo image
+  resource or a fallback URL. Handles remote URLs, page resources, and assets/media
+  lookups using the same rules as the inline per-item image resolver.
+
+  Inputs:
+    .path: image path (required) — relative ("dashboard.png", "media/foo.jpg")
+           or absolute URL ("https://…").
+    .Page: current page (optional, recommended for page-resource lookup).
+
+  Returns dict with one of:
+    .resource:     Hugo image resource (use with .Process, srcset, etc.)
+    .fallback_url: plain URL string (use as <img src>)
+  Or an empty dict if path is missing.
+*/}}
+{{ $result := dict }}
+{{ $path := strings.TrimSpace (printf "%v" (.path | default "")) }}
+
+{{ if $path }}
+  {{ $is_remote := or (strings.HasPrefix $path "http://") (strings.HasPrefix $path "https://") }}
+
+  {{ if $is_remote }}
+    {{ $remote := try (resources.GetRemote $path) }}
+    {{ if and $remote (not $remote.Err) }}
+      {{ $result = dict "resource" $remote.Value }}
+    {{ else }}
+      {{ $result = dict "fallback_url" $path }}
+    {{ end }}
+  {{ else }}
+    {{ $normalized := $path }}
+    {{ $normalized = strings.TrimPrefix "/" $normalized }}
+    {{ $normalized = strings.TrimPrefix "./" $normalized }}
+    {{ $normalized = strings.TrimPrefix "assets/" $normalized }}
+    {{ $normalized = strings.TrimPrefix "media/" $normalized }}
+    {{ $normalized = path.Clean $normalized }}
+
+    {{ if and $normalized (ne $normalized ".") }}
+      {{ $resource := false }}
+      {{ with .Page }}
+        {{ $resource = (.Resources.ByType "image").GetMatch $normalized }}
+      {{ end }}
+      {{ if not $resource }}
+        {{ $resource = resources.Get (path.Join "media" $normalized) }}
+      {{ end }}
+      {{ if $resource }}
+        {{ $result = dict "resource" $resource }}
+      {{ else }}
+        {{ $result = dict "fallback_url" (printf "/media/%s" $normalized) }}
+      {{ end }}
+    {{ end }}
+  {{ end }}
+{{ end }}
+
+{{ return $result }}