A tidier Performance tab, a fifth lab metric, and more precise medians

The site's Performance tab got a round of cleanup, plus one addition to the numbers themselves:

• The launch control is now a card, with the URL field in the body and Measure now in the footer, matching the card used to invite teammates on the members settings page.
• The tab is now split into Most recent run, Real-world field data (CrUX), and History, instead of one long stacked page. Switching between them is instant, and launching a new run no longer jumps you back to Most recent run if you were looking at Field data or History.
• The history table has a new Score (off → on) column, right after the URL. Hover it to see the full per-metric breakdown (performance score, LCP, CLS, TBT, and FCP, tag-off next to tag-on) without leaving the table.
• The CrUX field-data history is now a real table, most recent week first, instead of a collapsible text list: every week's LCP, CLS, INP, and TTFB side by side.
• LCP (largest contentful paint) joins the causal lab delta as a fifth metric, alongside the existing performance score, CLS, TBT, and FCP. It's parsed from the same PageSpeed Insights response the other four already come from, so it costs no extra API call. Runs measured before today show LCP as not measured, never as zero or an error.
• Each side of a run is now measured 5 times instead of 3, reduced to the median: a more stable number against PageSpeed Insights' normal run-to-run variance. All raw runs still stay visible behind the "based on N runs" toggle.