fix(log-viewer): show governor usage only where the log measured it

[lukecotter]

📝 PR Overview

The Inspector's Governor usage over time charts and the Timeline's governor strip read the same series, but drew it differently. The charts ran a straight line between two readings, which puts usage at instants the log never measured — plainest on CPU, whose only readings are the LIMIT_USAGE_FOR_NS and LIMIT_USAGE lines, so the invented climb between them spans most of the chart.

Each chart now steps like the strip: a reading stands until the next one. Two smaller disagreements go with it — the charts measured x against duration.total while the Timeline runs 0..exitStamp, so every reading sat right of where the Timeline drew it and a click seeked short of the instant picked; and the spans the log recorded nothing in, blanked on the strip in 1.22.0, were still filled straight across here.

🛠️ Changes made

• Step the trend line, and hold the hover readout to the reading before the cursor — no value is reported for an instant the log did not measure
• Measure x by exitStamp, the Timeline's own domain, so a reading sits where the Timeline draws it and click-to-seek lands on it
• Carry gaps on the shared series rather than adding them in the Timeline, so the charts leave unrecorded spans unfilled; the line still carries across one, because a governor total cannot fall
• Share recordedSegmentEnd between the strip and the charts, so the gap rule has one statement
• Memoise the marker extraction per log, which the series and the Timeline now both ask for
• Reframe inspector.png: the Analysis tab with a row selected, cropped to the panel, so the shot shows the Inspector on its own instead of repeating the Database tab

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality
• ♻️ Refactor - internal changes with no user impact
• ⚡ Performance Improvement
• 📝 Documentation - README or documentation site changes
• 🔧 Chore - dev tooling, CI, config
• 💥 Breaking change

📷 Screenshots / gifs / video [optional]

The 1.22 screenshot set is refreshed in the second commit. The chart change itself reads best live: open a log, Timeline tab, nothing selected, and compare the CPU chart against the strip below the flame chart.

🔗 Related Issues

N/A

✅ Tests added?

• 👍 yes

pnpm lint and pnpm exec jest --selectProjects log-viewer (2092 tests). New coverage: the step path, one fill shape per recorded stretch against an unbroken line, and the series carrying the log's gaps. The GovernorTrends fixture now sets exitStamp apart from duration.total, so reading the wrong one fails.

📚 Docs updated?

• 🔖 README.md
• 🔖 CHANGELOG.md
• 📖 help site
• 🧪 Marked any pre-release-only features
• 🙅 not needed

Anything else we need to know? [optional]

Two commits: the fix, then the screenshot work. Start at governorTrendData.ts (pointAt) and GovernorTrends.ts (trendPaths) — the rest follows from those.