Remove internal build decisions from visitor-facing content

The public site (and DOM) shouldn't advertise our tooling choices:

- Drop the design-system credit and typeface note from the footer; replace
  with visitor-useful copy ("Built to be sent" / "The canon")
- Remove the external-inspiration reference from the homepage lede
- Neutralize the meta description
- Rename the `cds-` CSS class prefix to `site-`
- Scrub internal names from source comments and the chart theme variable

Functional font-family references are kept; only the advertising is removed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XPEvmMbac2fCvKXpQcovj8

src/pages/index.astro

@@ -18,8 +18,7 @@ const sins = (await getCollection('sins', ({ data }) => !data.draft)).sort((a, b
     <p class="hero__lede">
       Don’t type the whole explanation for the hundredth time — send the link.
       Each sin shows the deceptive chart beside its honest twin, names the tell,
-      and cites the giants who back you up. It’s <a href="https://nohello.net" rel="noopener">nohello.net</a>,
-      for bad charts.
+      and cites the giants who back you up.
     </p>
   </section>