Top Tabs 0.5 on bb's restored navigation slot #74

Top Tabs 0.4.0 works around bb 0.46's rail with a React-context read, shell CSS overrides and a hand-run split drag. bb main restores a supported navigation slot, so most of that can go, and pinned tabs can show badges again.

Blocked on a bb release carrying get-bb/bb#5584 (merged 2026-10-16; in nightlies, not 0.46.1).

What #5584 gives (traced from the PR): experimental_sidebarNavigation with its pre-0.46 names and placement: "rail" | "list", the navigation, split and icon hooks, and an optional headerComponent. Badges arrive as item.badge. A provider with list placement brings back 0.45's layout (no rail column, footer Settings, collapse hides the sidebar) on supported hooks. Automatic picks the first installed provider.

Gains: retires plugins/top-tabs/lib/rail.ts's React-context read, most 0.46 shell CSS and the hand-run split drag.

Hazard: on the nightly, sidebar-footer-row and window-right-panel-toggle are gone, so 0.4.0's gear rule stops matching.

Acceptance: Top Tabs 0.5 registers a list provider, rail.ts is gone or reduced, pinned tabs show badges, and it works on the released bb.

Related: the nav counts badge issue, same bb release gate.