This pull request introduces a new interactive demos section to the site.

• adds a dedicated /demos/ page
• features a prominent demo on the homepage,
• links demos directly from relevant pattern pages.

This PR also includes some fixes and optimizations for Hugo build, which was taking too much time.

Interactive demos feature:

• Added a new content source (content/demos/_index.md) listing all available demos, their metadata, and next steps for users.
• Implemented a new /demos/ page (layouts/demos/list.html) that displays demos in a hero player with a sidebar playlist, using new partials for Arcade embed and demo selection cards. [1] [2] [3] [4]
• Added a featured interactive demo section to the homepage, showcasing a key demo with a direct embed and clear calls to action.

Pattern page integration:

• Linked the relevant demo to each pattern's metadata (demo: in the links: section) so that pattern pages can reference their associated interactive walkthrough. [1] [2] [3] [4] [5] [6]

Performance improvements:

• Switched from partial to partialCached for the footer.html partial in all major layouts, reducing redundant template rendering and improving page load times. [1] [2] [3] [4] [5] [6] [7] [8] [9]

These changes collectively enhance the discoverability and usability of interactive demos, streamline the user journey from patterns to demos, and optimize site performance.