Add marks for compression experiment

Author: csswizardry

_includes/header--masthead.html

@@ -11,12 +11,14 @@
 
 {% include ribbon.html %}
 
+<script>performance.mark('beforeIMG')</script>
 <header class="page-head  page-head--masthead" elementtiming=masthead>
 
     <div class=wrapper>
 
         {% include nav.html %}
 
+        <script>performance.mark('beforeH1')</script>
         <h1 class=page-head__text elementtiming=mastheadTitle>{{ page.masthead-title }}</h1>
 
         <h2 class=hide>Proven results improving Core Web Vitals for world-leading organisations.</h2>

_layouts/page.html

@@ -10,6 +10,7 @@
         <main class="layout__item  desk-three-fifths" data-ui-component="Main content" id="section:main">
           <script>performance.mark('contentStart')</script>
 
+            <script>performance.mark('beforeH1')</script>
             <h1 elementtiming="page-title">{{ page.title }}</h1>
 
             {% if page.path contains ".md" %}

_layouts/post.html

@@ -34,6 +34,7 @@
 
         </p>
 
+          <script>performance.mark('beforeH1')</script>
           <h1 itemprop="name  headline" elementtiming=page-title style="view-transition-name: x-{{ page.date | date: '%Y-%m-%d' }}">{{ page.title }}</h1>
 
           <p class=hide>Written by <b itemprop=author>Harry Roberts</b> on <b itemprop=publisher>CSS Wizardry</b>.</p>

about.md

@@ -27,6 +27,7 @@ teams around the world. Heard enough?
 
 <a href="/contact/" class="btn  btn--full  btn--positive">Hire me!</a>
 
+<script>performance.mark('beforeIMG')</script>
 <figure>
   <img src="/img/content/about.jpg"
        alt="Harry Roberts leading a web performance workshop at Digital Labin 2022, standing in front of a group of attendees and speaking with animated hand gestures against a concrete and tiled backdrop."

consultancy.md

@@ -55,6 +55,7 @@ issues. Together, we answer questions such as:
 
 It’s my job to help you find the answers.
 
+<script>performance.mark('beforeIMG')</script>
 <figure>
   <img src="/img/content/consultancy.jpg"
        alt=""

speaking.md

@@ -14,6 +14,7 @@ I’ve spoken at [over one-hundred conferences](#section:past-events). Sharing
 practical knowledge is one of my key motivations. It’s also a large part of why
 I became a consultant in the first place — I love to help.
 
+<script>performance.mark('beforeIMG')</script>
 <figure>
   <img src="/img/content/perfnow-2024.jpg"
        alt="Harry Roberts delivering a keynote on stage at performance.now() 2024 in Amsterdam, photographed mid-talk in front of a large projected slide."

workshops.md

@@ -26,6 +26,7 @@ With a 99% approval rating, my workshops are not your typical corporate training
 session. They’re intense, intensive, and packed with real-world, practical
 insights. I’m a teacher who _does_.
 
+<script>performance.mark('beforeIMG')</script>
 <figure>
   <img src="/img/content/workshops.jpg"
        alt=""