fix(site): give the Config Builder the sidebar back

It used `template: splash`, which is Starlight's no-sidebar layout — so the
one page a first-timer is sent to from Start Here was also the only page in
the site with no way to navigate onward.

Dropping splash needs two things with it. Starlight's default content column
is 45rem, sized for prose, which would have collapsed the wizard's form and
YAML preview into a single column on every screen; ConfigWizard.astro widens
it to 82rem. And the page has no headings, so the table of contents would
have rendered empty — disabled in frontmatter.

The width override is a `:root` rule inside the component's style block.
Astro leaves `:root` unscoped, and code-splits the CSS per page, so it lands
only on the one page that renders the component — verified: the rule ships in
config-builder.*.css and no other page loads that file.

Verified in the built site: sidebar renders with Config Builder active, and
the wizard keeps its two 588px columns.

Claude-Session: https://claude.ai/code/session_01RgSnMCa3JQigphGnPbazdw

Author: RAR

docs/images/Dashboard.png

@@ -99,6 +99,17 @@
 </script>
 
 <style>
+  /* This component renders on exactly one page, so a global rule here is
+     page-scoped in practice. Starlight's 45rem default is sized for prose and
+     would force the form and its YAML preview into a single column on every
+     screen; the wizard is a two-pane tool, not an article. */
+  :root {
+    --sl-content-width: 82rem;
+  }
+  /* Starlight caps the prose column; the wizard needs the full width it was
+     just given, and its own max-width still governs the upper bound. */
+  .sl-markdown-content .tigo-wizard { max-width: none; }
+
   .tigo-wizard {
     display: grid;
     grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);

docs/images/Diagnostics.png

@@ -1,7 +1,10 @@
 ---
 title: Config Builder
 description: Generate a ready-to-flash ESPHome YAML for your Tigo Monitor board, right in the browser.
-template: splash
+# Not `template: splash` — splash is the no-sidebar layout, which left this page
+# as the only one in the site with no way to navigate back out. The wizard needs
+# a wider content column than the 45rem default; ConfigWizard.astro widens it.
+tableOfContents: false
 ---
 
 import ConfigWizard from '../../components/ConfigWizard.astro';