fix(tauri): update @reserved annotations + remove dead SaaS client methods

- Update 9 @reserved → @connected for commands with frontend consumers:
  zclaw_status, zclaw_start, zclaw_stop, zclaw_restart, zclaw_doctor,
  viking_add_with_metadata, viking_store_with_summaries,
  trigger_execute, scheduled_task_create
- Remove 10 dead SaaS client methods with zero callers:
  healthCheck, listDevices (saas-client.ts)
  getRelayTask, getUsage/relay (saas-relay.ts)
  listPrompts, getPrompt, listPromptVersions, getPromptVersion (saas-prompt.ts)
  getPlan, getUsage/billing (saas-billing.ts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/lib/saas-billing.ts

@@ -9,7 +9,6 @@
 import type {
   BillingPlan,
   SubscriptionInfo,
-  UsageQuota,
   CreatePaymentRequest,
   PaymentResult,
   PaymentStatus,
@@ -80,14 +79,6 @@ export function installBillingMethods(ClientClass: { prototype: any }): void {
     return this.request<BillingPlan[]>('GET', '/api/v1/billing/plans');
   };
 
-  /** Get a single plan by ID */
-  proto.getPlan = async function (
-    this: { request: RequestFn },
-    planId: string,
-  ): Promise<BillingPlan> {
-    return this.request<BillingPlan>('GET', `/api/v1/billing/plans/${planId}`);
-  };
-
   // --- Subscription ---
 
   /** Get current subscription info (plan + subscription + usage) */
@@ -97,15 +88,6 @@ export function installBillingMethods(ClientClass: { prototype: any }): void {
     return this.request<SubscriptionInfo>('GET', '/api/v1/billing/subscription');
   };
 
-  // --- Usage ---
-
-  /** Get current month's usage quota */
-  proto.getUsage = async function (
-    this: { request: RequestFn },
-  ): Promise<UsageQuota> {
-    return this.request<UsageQuota>('GET', '/api/v1/billing/usage');
-  };
-
   // --- Payments ---
 
   /** Create a payment order for a plan upgrade */