Replace the overlapping usage and cost model with canonical billing
primitives centered on ModelRef, ModelHandle, TokenCounts, and
BilledModelUsage. This also renames the public API and web surface from
usage to billing, removes compatibility aliases, and normalizes provider
usage adapters onto the shared billing vocabulary.
These endpoints had zero CLI callers and served only the web UI demo.
Verification and retros were `not_implemented` stubs in real mode;
sessions had an in-memory implementation but no CLI usage. Removing
them shrinks the API surface and eliminates ~9,000 lines of dead code.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Dead feature cleanup: `skill install` was hidden/experimental and never
graduated; the run verification endpoint was only implemented in demo mode.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Move the browser sign-in page off the backend /auth namespace so direct
navigation works, update Rust and frontend redirects to /login, and add
tests that lock the split between SPA login UI and backend OAuth endpoints.
Replace the old React Router SSR setup with a static SPA build served by
fabro-server, move setup and GitHub auth handling into Rust, and update the
default local web URL and stale Arc-era references to match the Fabro name.
