UX/perf: touch parity, throttling, workerized connectivity

[fluffyrabbot]

Summary

• Improve touch UX and prevent scroll bleed: DRC popovers, dimension tool, edit overlays (trace/placement) now handle touch start/move/end and set touchAction to avoid page scroll during drags.
• Reduce pointer churn: pointer move paths are throttled via requestAnimationFrame (mouse tracker, dimension overlay, edit overlays) to cut render-time spikes on hover/drag.
• Keep overlays visible: toolbar z-index uses the shared map; tooltip and menu layers stay above pads/traces.
• Offload heavy nets: rats-nest/connectivity map building runs in a web worker; canvas renderer consumes the plain data, reducing main-thread stalls on large designs.
• Harden Cosmos fixtures: wrap fixtures with store/providers, ignore asset-only files, generate circuitJson where missing, and default the perf-stress fixture to a lighter grid (toggleable for full stress) so preview doesn’t hang.

Test Plan

• bun run build
• Cosmos: open canvas renderer, macro keypad, perf stress (default small grid), DRC/error overlays; verify they render without errors and remain responsive on touch and mouse.

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Project	Deployment	Preview	Comments	Updated (UTC)
pcb-viewer	Ready	Preview	Comment	Dec 8, 2025 4:54am

[rushabhcodes]

For future work, please keep PRs scoped to one area at a time. This one combines UX fixes, performance changes, z-index rework, and fixture updates, which makes it harder to review, reason about, and revert if needed. Smaller, focused PRs will be easier to land and maintain.