perf(docs): cache Hugo template partials for 29% faster builds

Add partialCached to three hot paths identified via --templateMetrics. head-css.html: SCSS compilation was repeated for all 860+ pages despite identical output. Pass .Site as context so partialCached shares a single cache entry (100% hit rate, was 0%). structureddata.looker.html: iterated ALL site pages to build a title list on every page render, O(n^2) total work. Extract the computation into a cached capital-titles.html partial (84s to 4s). sidebar.html: SVG chevron icon was loaded, minified, and string-replaced inside the recursive nav template (~15k invocations). Extract into cached chevron-svg.html partial (100% hit rate). Verified locally: before/after HTML output is byte-identical (diff -rq). Build time on 864 pages: 18.5s to 13.1s (29% faster).

JIRA: trivial
risk: nonprod

Author: hkad98

docs/layouts/partials/chevron-svg.html

@@ -0,0 +1,4 @@
+{{/* Cached chevron SVG icon — loaded and minified once per build. */}}
+{{- $icon := resources.Get "icons/chevron-menu.svg" -}}
+{{- $svg := $icon | minify -}}
+{{- return (replace $svg.Content "<svg " "<svg aria-hidden=\"true\" focusable=\"false\" ") -}}

docs/layouts/partials/head-css.html

@@ -1,6 +1,6 @@
 
 {{ $scssMain := "scss/main.scss"}}
-{{ if .Site.IsServer }}
+{{ if .IsServer }}
 {{/* Note the missing postCSS. This makes it snappier to develop in Chrome, but makes it look sub-optimal in other browsers. */}}
 {{ $css := resources.Get $scssMain | toCSS (dict "enableSourceMap" true) }}
 <link href="{{ $css.RelPermalink }}" rel="stylesheet">

docs/layouts/partials/head.html

@@ -20,7 +20,7 @@
 {{- template "_internal/schema.html" . -}}
 {{- template "_internal/twitter_cards.html" . -}}
 
-{{ partialCached "head-css.html" . "asdf" }}
+{{ partialCached "head-css.html" .Site "head-css" }}
 <script
   src="https://code.jquery.com/jquery-3.5.1.min.js"
   integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0="

docs/layouts/partials/sidebar.html

@@ -70,11 +70,7 @@
                       aria-controls="section-{{ $pageId }}"
                       aria-label="{{ if $activeSection }}Collapse{{ else }}Expand{{ end }} {{ $page.LinkTitle }} section">
                       <span class="gd-docs-menu-page__chevron">
-                        {{ with resources.Get "icons/chevron-menu.svg" }}
-                          {{ $svg := . | minify }}
-                          {{ $svg := replace $svg.Content "<svg " "<svg aria-hidden=\"true\" focusable=\"false\" " }}
-                          {{ $svg | safeHTML }}
-                        {{ end }}
+                        {{ partialCached "chevron-svg.html" . "chevron" | safeHTML }}
                       </span>
                     </button>
                 {{ end }}

docs/layouts/partials/structureddata/capital-titles.html

@@ -0,0 +1,23 @@
+{{/* Returns a slice of unique, capitalized page titles from the site.
+     Called via partialCached — computed once per build, not per page. */}}
+{{- $pageTitles := slice -}}
+{{- range .Pages -}}
+  {{- $pageTitles = $pageTitles | append .Title -}}
+{{- end -}}
+
+{{- $uniquePageTitles := slice -}}
+{{- range $pageTitles -}}
+  {{- if not (in $uniquePageTitles .) -}}
+    {{- $uniquePageTitles = $uniquePageTitles | append . -}}
+  {{- end -}}
+{{- end -}}
+
+{{- $capitalTitles := slice -}}
+{{- range $uniquePageTitles -}}
+  {{- $firstChar := substr . 0 1 -}}
+  {{- if eq $firstChar (upper $firstChar) -}}
+    {{- $capitalTitles = $capitalTitles | append . -}}
+  {{- end -}}
+{{- end -}}
+
+{{- return $capitalTitles -}}

docs/layouts/partials/structureddata/structureddata.looker.html

@@ -1,30 +1,7 @@
 {{- $pageData := .Page -}}
 {{- $siteData := .Site -}}
 
-{{- $sectionTitles := slice -}}
-{{- range $siteData.Sections -}}
-{{- $sectionTitles = $sectionTitles | append .Title -}}
-{{- end -}}
-
-{{- $pageTitles := slice -}}
-{{- range $siteData.Pages -}}
-{{- $pageTitles = $pageTitles | append .Title -}}
-{{- end -}}
-
-{{- $uniquePageTitles := slice -}}
-{{- range $pageTitles -}}
-{{- if not (in $uniquePageTitles .) -}}
-    {{- $uniquePageTitles = $uniquePageTitles | append . -}}
-{{- end -}}
-{{- end -}}
-
-{{- $capitalTitles := slice -}}
-{{- range $uniquePageTitles -}}
-{{- $firstChar := substr . 0 1 -}}
-{{- if eq $firstChar (upper $firstChar) -}}
-    {{- $capitalTitles = $capitalTitles | append . -}}
-{{- end -}}
-{{- end -}}
+{{- $capitalTitles := partialCached "structureddata/capital-titles.html" $siteData "capital-titles" -}}
 
 {{ if in $capitalTitles $pageData.Params.title }}
  {{ if eq $pageData.Params.title "Introduction" }}