Fix reference sidebar flash by server-rendering directory

[rakesh2OO5]

Summary

This PR fixes a visible flash and layout instability on the reference page by server-rendering the reference directory instead of relying solely on client-side hydration.

What changed

• Added a server-rendered Astro component for the reference directory
• Kept ReferenceDirectoryWithFilter as a client-side enhancement for filtering/search
• Updated ReferenceLayout to render the directory during SSR

Why

The reference page previously rendered its directory only after client hydration, causing a noticeable flash and layout shift. Rendering the directory on the server ensures stable initial HTML and eliminates the flash.

Result

• Reference page content is present immediately on load
• No flash or temporary disappearance
• Filtering behavior remains unchanged

Testing

• Verified reference page renders immediately without flash
• Tested with JavaScript disabled to confirm SSR output
• Confirmed reference navigation and routing continue to work

Notes

• Console warnings related to service workers or external scripts are pre-existing and unrelated
  Fixes Consider using transitions or reduce use of JS in the nav links #477