#9956 improvement(desktop-browser): click through a nested control that fills the whole target

Summary

• browser_click on a target whose whole area is one nested control (a time-slot label filling its link) now clicks there — what a person clicking the target hits — and reports clickedThrough, instead of refusing with "lands on X, which is its own control inside that element"
• A nested control covering only part of the target still refuses, so a card's own Save/heart button is never hit by a click meant for the card

Type of Change

• Improvement

Testing

• Red/green unit tests in page-functions.test.ts (fills-the-target clicks through; partial cover still refuses); 541 browser-agent tests pass
• Production-loop benchmark on REAL (Opus 5.5, Sim's Electron driver, 242 paired episodes, both arms concurrent, fresh seeds): nested-control refusals 42 → 0; on the episodes where it fired, rounds −17% and wall −24% with success unchanged. Suite-wide success 156 → 152 is noise — none of the lost episodes involved a click-through

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)