Replace per-handler `token string` field with package-level
`pkgGatewayToken` via `InitGatewayToken()`, matching the existing
pattern for `pkgAPIKeyCache`, `pkgOwnerIDs`, etc.
- Remove `token` from ~30 HTTP handler structs and constructors
- Simplify `requireAuth(minRole, next)` signature (was 3 params)
- Simplify `resolveAuth(r)` signature (was 2 params)
- Rename `resolveAuthBearer` → `resolveAuthWithBearer` (clearer)
- Add `store.WithRole()`/`RoleFromContext()` to propagate caller
role through context
- Inject role into context in `requireAuth` and `requireAuthBearer`