garden: sessions redundancy + theme toggle + no toggle reveal

- Sessions list: no tag header, stripped 'Vigo Session Log:' prefix
- Session single: flat sections instead of fragment toggle (details/summary)
- Theme toggle: explicit font-family + color ensures emoji icon renders
- New: layouts/sessions/list.html, sessions/single.html
- Changed: content/sessions/*.md (no fragment shortcodes), garden.css

layouts/sessions/single.html

@@ -0,0 +1,33 @@
+{{ define "main" }}
+<article>
+  <header>
+    <hgroup>
+      <h1>{{ .Title | replaceRE "^Vigo Session Log: " "" }}</h1>
+      {{- if not .Date.IsZero }}
+      <p data-text="dim"><time datetime="{{ .Date.Format "2006-01-02" }}">{{ .Date.Format "January 2, 2006" }}</time></p>
+      {{- end }}
+    </hgroup>
+
+    {{- with .GetTerms "tags" }}
+    <nav data-role="tag-cloud" aria-label="Tags">
+      {{- range . }}
+      <a href="{{ .Permalink }}" data-tag="{{ .Name }}">{{ .Name }}</a>
+      {{- end }}
+    </nav>
+    {{- end }}
+  </header>
+
+  {{ .Content }}
+
+  {{- if or .PrevInSection .NextInSection }}
+  <footer>
+    {{- with .PrevInSection }}
+    <a href="{{ .RelPermalink }}" rel="prev" data-wikilink>← {{ .Title | replaceRE "^Vigo Session Log: " "" }}</a>
+    {{- end }}
+    {{- with .NextInSection }}
+    <a href="{{ .RelPermalink }}" rel="next" data-wikilink>{{ .Title | replaceRE "^Vigo Session Log: " "" }} →</a>
+    {{- end }}
+  </footer>
+  {{- end }}
+</article>
+{{ end }}