Bound serve_stale member copies by age, toggle and eviction

- drop a member's copy when serve_stale is off
- block on the member again once its copy is over an hour old
- skip storing a refresh whose entry was evicted or replaced
- show serve_stale in the UI and TUI

ui/src/api/types.ts

@@ -17,6 +17,7 @@ export interface Remote {
   quarantine_enabled: boolean;
   quarantine_days: number;
   stale_on_error: boolean;
+  serve_stale: boolean;
   releases_remote: string;
   managed_by: string;
   created_at: string;

ui/src/pages/RemoteDetail.tsx

@@ -50,6 +50,8 @@ export function RemoteDetail() {
             <dd>{remote.check_mutable ? 'enabled' : 'disabled'}</dd>
             <dt>Stale on Error</dt>
             <dd>{remote.stale_on_error ? 'enabled' : 'disabled'}</dd>
+            <dt>Serve Stale</dt>
+            <dd>{remote.serve_stale ? 'enabled' : 'disabled'}</dd>
             {remote.releases_remote && (
               <>
                 <dt>Releases Remote</dt>