[Frontend UX] Reorder sidebar navigation around primary workflows

[libby-coder]

Summary

• Reorders NAV_LINKS to place primary workflow actions first: Dashboard → Swap → Marketplace → Orders → Explorer (Activity)
• Adds a horizontal divider between primary and secondary groups in both desktop Sidebar and mobile Drawer
• Secondary/admin/info routes follow the divider: HTLCs → Protocol → Settings → About → Admin
• Exports PRIMARY_NAV_LINKS and SECONDARY_NAV_LINKS from navigation.ts for grouped render; flat NAV_LINKS kept for other consumers
• Mobile drawer mirrors the exact same order and grouping as the desktop sidebar

Test plan

• Desktop sidebar shows Dashboard, Swap, Market, Orders, Explorer at the top, then a divider, then HTLCs, Protocol, Settings, About (Admin only for admins)
• Mobile drawer reflects the same order and grouping
• Active-state indicator and aria-current="page" still work on all links in both groups
• Admin link still hidden for non-admin users

Closes #407
Closes #408
Closes #409
Closes #417

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