Add Discord and Manual links to website sticky menu

[Copilot]

Adds community Discord link (https://discord.gg/p4J5zVSe) to the website navigation menu alongside a new Manual link for the quickstart PDF.

Changes

• Sticky menu additions in docs/themes/zeptocore/layouts/_default/baseof.html:

  • Manual link → /img/zeptocore_quickstart.pdf (book icon)
  • Discord link → community invite (Discord icon)
  • Both positioned after Firmware in left sidebar

• Security/accessibility: Links include rel="noopener noreferrer" and aria-label attributes for external navigation

Preview

Both links open in new tabs and appear in the sticky menu after scrolling.

Original prompt

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This section details on the original issue you should resolve

<issue_title>add link</issue_title>
<issue_description>In core, in website, to the right of the manual link put a icon and link to join the discord: Add a button to link to the discord! https://discord.gg/p4J5zVSe</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes add link #808

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