Fix tooltip visibility and expand color palette (fixes #196)

[emeryberger]

Summary

• Expand color palette from 4/5 to 8 colors — legend icons used % 4 and plot series used % 5, but CSS defines 8 distinct series colors. Both now use % 8 so all colors (indigo, emerald, rose, amber, violet, cyan, pink, lime) are utilized.
• Add progress point name to tooltip — hovering a data point now shows which progress point it belongs to, not just the speedup values.
• Fix tooltip positioning — tooltips were rendered off-screen when progress point paths were long (e.g. /Users/.../linear_regression-pthread.c:86 made the tooltip 590px wide). Fixed by: passing the SVG circle element directly to d3-tip (tip.show(d, this) instead of tip.show(d, i)), truncating paths to just filename:line in the tooltip, and adding max-width: 320px with word-wrap as a safety net.

Closes #196

Test plan

• Selenium test confirms all circles show tooltip on hover with opacity=1, within viewport
• Tooltip content shows "Progress Point: linear_regression-pthread.c:86" (filename only, not full path)
• Tooltip width is 297px (was 590px before), fits within plot area
• Verified with both sqlite.coz (many plots, 1 progress point) and linear_regression profile (4 data points, long path)

🤖 Generated with Claude Code

[ebkalderon]

Seems to work pretty well! Tested locally on a Rust application with 11 progress points, and the UI looks much clearer. I'm especially happy to see the in-tooltip filenames originally from #169 have returned. Thanks for addressing this, @emeryberger. 🎉