fix: highlight same-net schematic traces on hover

[wpearce1]

/claim tscircuit/tscircuit#1130
/fixes tscircuit/tscircuit#1130

Summary

Adds same-net hover highlighting for schematic traces in @tscircuit/schematic-viewer.

• Adds useTraceNetHoverHighlight, using event delegation on the generated SVG.
• Groups rendered schematic traces by electrical connectivity, not just the hovered DOM element:
  • explicit net ids on traces/ports
  • source_net relationships
  • shared connected source ports
  • fallback to the individual source trace when no net metadata is present
• Highlights all visible trace paths in the hovered net and restores their original stroke/stroke-width on mouseout.
• Skips invisible hover outlines and crossing outlines so only actual trace strokes change.
• Adds a Cosmos fixture with multiple traces on net.VOUT and net.GND for manual verification.

Test plan

• npm install --package-lock=false --legacy-peer-deps (local only; repo normally uses Bun but this machine does not have bun installed)
• npx biome format .
• npx -p typescript@^5.0.0 tsc --noEmit
• git diff --check

Notes

The existing open PR #182 appears to group by source_trace_id; this PR goes a bit broader and unions traces by same-net metadata so separate trace segments connected through net.* labels highlight together as requested.

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Project	Deployment	Actions	Updated (UTC)
schematic-viewer	Ready	Preview, Comment	May 11, 2026 2:07am