Add the server-side CLI OAuth endpoints and token persistence needed to
mint JWT access tokens and rotating refresh tokens from the existing
GitHub web auth flow.
Add CLI auth storage plus `fabro auth login`, `logout`, and `status`, and
prefer stored OAuth access tokens when building target clients.
Add the shared fabro-http transport crate and route hand-written HTTP client construction through it.
Use FABRO_HTTP_PROXY_POLICY for test no-proxy defaults, remove direct reqwest deps from ordinary crates, and add clippy bans for raw reqwest entrypoints.
Add the stripped twin-github test server to the workspace, wire it through
fabro-test, and cover fabro-github's real HTTP auth and pull-request flows
with twin-backed integration tests. This also refactors the GitHub helper
entry points to take explicit base URLs so tests and callers share the same
request path.
