[Epic] Expand dashboard to full bootc ecosystem image tabs

[castrojo]

Goal

Restructure the dashboard navigation and data pipeline to cover the full bootc ecosystem, not just ublue-os consumer images.

Taxonomy (confirmed)

Universal Blue tab = ublue-os/main + ublue-os/akmods (base infra only)

Consumer images each get a dedicated top-level tab:

• Bluefin (existing /builds/)
• Aurora (existing /aurora-builds/)
• Bazzite (existing /bazzite-builds/)
• uCore (new — GitHub/registry metrics only, no countme; uCore reports os_name='Fedora Linux')
• secureblue (new — countme os_name: secureblue, 179K hits)
• wayblue (new — countme os_name: wayblue, 45K hits)
• BlueBuildOS (new — countme os_name: BlueBuildOS, 17K hits)

Countme threshold: >=10,000 recent hits

Images excluded (below threshold or data indistinguishable):

• CentOS Stream bootc: reports os_name='CentOS Stream', indistinguishable from 119M base OS users — skip
• winblues org images (winblues7, blue95, blue9): below threshold in countme
• toxicblue (7.4K), Bluefin LTS (6.8K), risiOS (5.9K): below threshold

Child issues

• Issue 72: Expand countme validDistros in Go backend
• Issue 73: Universal Blue tab
• Issue 74: uCore tab
• Issue 75: secureblue tab
• Issue 76: wayblue tab
• Issue 77: BlueBuildOS tab

Notes

• Per-image breakdown on each tab = countme os_name values only (no recipe-level splitting)
• secureblue: all variants (cosmic, kinoite, iot, securecore) roll up to single 'secureblue' os_name
• wayblue: all compositor images (hyprland, niri, sway, river, qtile, wayfire) roll up to single 'wayblue' os_name