Default MCP tab tools to the active tab

Requiring an explicit tab_id forced every navigate or close through a
preceding tabs_list call, which costs an MCP client a full round trip just to
learn the ID the browser already considers current.

navigate and tabs_close now resolve the active tab when tab_id is omitted,
matching the screenshot tool. Resolution is explicit rather than forwarding
None into the SDK, so the acting tool knows which tab it touched; tabs_close
reports it, since closing the wrong tab is not recoverable.

This stays in the MCP layer: the SDK and CLI signatures are unchanged.

extension/src/commands/perf.ts

@@ -1,7 +1,7 @@
 import { getLargeOperationThrottle, getPerformanceProfile, hasAudibleTabs, setPerformanceProfile } from '../core';
 import { CommandGroup } from '../classes/CommandGroup';
 import type { CommandEntry } from '../classes/CommandGroup';
-import type { PerfSetProfileArgs, JobIdArgs } from '../types';
+import type { Job, PerfSetProfileArgs, JobIdArgs } from '../types';
 
 // PerfCommands also owns the jobs.* status/cancel queries: they read the same
 // JobManager (ctx.jobs) that perf.status reports, and there is no dedicated
@@ -15,6 +15,19 @@ export class PerfCommands extends CommandGroup {
     "jobs.cancel":      (a: JobIdArgs) => this.ctx.jobs.cancel(a),
   };
 
+  private jobSummary(job: Job) {
+    return {
+      id: job.id,
+      command: job.command,
+      status: job.status,
+      phase: job.phase,
+      current: job.current,
+      total: job.total,
+      percent: job.percent,
+      cancelRequested: job.cancelRequested,
+    };
+  }
+
   private async perfStatus() {
     const profile = await getPerformanceProfile();
     const audible = await hasAudibleTabs();
@@ -23,16 +36,7 @@ export class PerfCommands extends CommandGroup {
       performanceProfile: profile,
       audible,
       throttle,
-      jobs: this.ctx.jobs.list().map(job => ({
-        id: job.id,
-        command: job.command,
-        status: job.status,
-        phase: job.phase,
-        current: job.current,
-        total: job.total,
-        percent: job.percent,
-        cancelRequested: job.cancelRequested,
-      })),
+      jobs: this.ctx.jobs.list().map(job => this.jobSummary(job)),
     };
   }
 }