Fragment shortcode + session log template (garden#6)

New shortcode: {{< fragment type="dialogue" label="..." >}}...{{< /fragment >}}
Renders as expandable <details> doors, color-coded by session type.
Full CSS for fragments in garden.css: dot, door label, session ID,
tinted background on open.

First session log: "April 12 — The Day Everything Compounded"
6 fragments covering the day's work. The context.html format
made reusable as a Hugo writing pattern.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

layouts/shortcodes/fragment.html

@@ -0,0 +1,14 @@
+{{- $type := .Get "type" | default "dialogue" -}}
+{{- $session := .Get "session" | default "" -}}
+{{- $label := .Get "label" | default "" -}}
+{{- $open := .Get "open" | default false -}}
+<details class="fragment" data-type="{{ $type }}"{{ with $session }} data-session="{{ . }}"{{ end }}{{ if $open }} open{{ end }}>
+  <summary>
+    <span class="dot"></span>
+    <span class="door">{{ $label }}</span>
+    {{ with $session }}<span class="session-id">S{{ . }}</span>{{ end }}
+  </summary>
+  <div class="fragment-content">
+    {{ .Inner | markdownify }}
+  </div>
+</details>