feat(cli): add codegraph usage command to show AI balance and recent usage

Adds a `usage` subcommand that pings `/v1/usage` with the stored token and
displays balance, plan, 30-day explore/token counts, and allowance reset date.

Degrades quietly in all non-happy-path states — signed out, BYO endpoint, or
unreachable server — so managed reasoning remaining optional doesn't change.

Also extends `OffloadUsage` with the fields the endpoint already returns
(`unlimited`, `banned`, `tokensLast30`, `callsLast30`, `creditsLast30`) that
were previously untyped.

src/reasoning/reasoner.ts

@@ -47,6 +47,11 @@ export interface OffloadUsage {
   overage?: number;
   remaining?: number;
   periodEnd?: number;
+  unlimited?: boolean;
+  banned?: boolean;
+  tokensLast30?: number;
+  callsLast30?: number;
+  creditsLast30?: number;
   models?: string[];
 }