feat: implement Tier 3 features — lane queue, credential redaction, token dashboard, xAI, Voyage AI

- Lane Queue: per-session FIFO queue in gateway replacing reject-when-busy (9 tests)
- Credential Redaction: redactConfig() expanded to cover 18+ secret fields (16 tests)
- Web UI Token Dashboard: system.tokenUsage endpoint + Usage page with summary cards
- xAI (Grok) Provider: OpenAI-compatible client with model pricing
- Voyage AI Embeddings: new embedding provider with configurable dimensions (5 tests)
- Update gap analysis: 90→95 match (70%→74%), Tier 3 section marked DONE
- Update state.json: test count 1001→1034, add tier3_completion entry

Total: 1034 tests passing across 85 files, typecheck clean

src/gateway/server.ts

@@ -5,6 +5,7 @@ import { Router } from './router.js';
 import { serveStatic } from './static.js';
 import { SessionBridge } from './session-bridge.js';
 import type { SessionBridgeConfig } from './session-bridge.js';
+import { LaneQueue } from './lane-queue.js';
 import { authenticateRequest } from './auth.js';
 import type { AuthConfig } from './auth.js';
 import {
@@ -20,6 +21,7 @@ import {
   createAgentHandlers,
   createConfigHandlers,
 } from './handlers/index.js';
+import type { TokenUsageEntry } from './handlers/system.js';
 import type { SessionManager } from '../session/manager.js';
 import type { Config } from '../config/index.js';
 import type { ToolRegistry } from '../tools/registry.js';
@@ -48,6 +50,8 @@ export interface GatewayServerConfig {
   webhookHandler?: WebhookHandler;
   /** Optional Gmail handler for Pub/Sub push notifications. */
   gmailHandler?: GmailWatcher;
+  /** Optional callback to retrieve per-session token usage data for the dashboard. */
+  getTokenUsage?: () => TokenUsageEntry[];
 }
 
 export class GatewayServer {
@@ -55,6 +59,7 @@ export class GatewayServer {
   private httpServer: HttpServer | null = null;
   private router: Router;
   private sessionBridge: SessionBridge;
+  private laneQueue: LaneQueue;
   private connectionMap: Map<WebSocket, string> = new Map();
   private config: GatewayServerConfig;
   private startTime: number = Date.now();
@@ -70,6 +75,7 @@ export class GatewayServer {
       toolExecutor: config.toolExecutor,
     });
 
+    this.laneQueue = new LaneQueue();
     this.router = new Router();
     this.registerHandlers();
   }
@@ -89,6 +95,7 @@ export class GatewayServer {
         totalSessions: this.config.sessionManager.listSessions().length,
         activeConnections: this.sessionBridge.connectionCount,
       }),
+      getTokenUsage: this.config.getTokenUsage,
     });
 
     const sessionHandlers = createSessionHandlers({
@@ -103,6 +110,7 @@ export class GatewayServer {
 
     const agentHandlers = createAgentHandlers({
       sessionBridge: this.sessionBridge,
+      laneQueue: this.laneQueue,
     });
 
     // Config handlers (only if config object is provided)