Show 3D switch in 2D header and update GitHub link

[jackiectl2]

What changed

• Add a 3D Website link to the Hugo navigation and move it beside Search when JavaScript runs, so the switch is visible in the sticky header and has a menu fallback.
• Point the site's GitHub icon to jackiectl2 and preserve this link when the profile sync script runs.
• Update the downloadable CV PDF so its printed GitHub address and clickable hyperlink both point to jackiectl2. The PDF body text is unchanged.

Verification

• Hugo build, JavaScript syntax check, and git diff check passed.
• Local browser confirmed the header switch and GitHub icon URLs after entering the 2D site.
• Rebuilt and visually checked all three PDF pages; verified the PDF text and hyperlink target.