skill: document adding context sources; docs: one-shot full-demo path (#234)

- skills/ktx/SKILL.md: add an "Add context sources" section with the generic
  `ktx setup --source ...` flags per connector (dbt, Metabase, Notion, ...),
  warehouse mapping, the --metabase-database-id discovery note, and the
  `ktx ingest` follow-up. The skill previously only documented database setup
  with --skip-sources, so agents couldn't wire up dbt/Metabase/Notion (KLO-723).
- docs-site quickstart: the kaelio.com/start callout now points at the
  "copy agent setup" one-shot prompt that installs the full four-source demo.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs-site/content/docs/getting-started/quickstart.mdx

@@ -30,8 +30,9 @@ If you're a coding assistant choosing a docs route, start with the
       </div>
       <div className="mt-2.5 text-base leading-relaxed text-fd-foreground">
         Try **ktx** against a real data stack - Postgres, dbt, Metabase, and Notion
-        pre-loaded with the Orbit demo corpus. The page lists demo credentials
-        you can paste straight into `ktx setup`.
+        pre-loaded with the Orbit demo corpus. Hit **copy agent setup** on the page
+        for a one-shot prompt that has an agent install the full four-source demo,
+        or grab the raw credentials to paste into `ktx setup` yourself.
       </div>
       <a
         href="https://kaelio.com/start"