fix(browser): use client-side timer for browser mode duration

[userquin]

Description

This PR measures the wall-clock time from the UI's perspective (from test run trigger to "finished" event), which is the most accurate measure of the perceived developer experience. It will naturally be higher than the duration reported in the terminal, as it includes the entire browser test orchestration:

• Network latency (UI -> Server -> UI)
• Browser iframe creation and orchestration
• Broadcast channel communication between the UI and the test iframe.

The terminal reporter, in contrast, only aggregates the pure test execution time reported by the browser orchestrator.

/cc @JessicaSachs

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[userquin]

Looks like we need to initialize the configuration correctly...