Fix topology route clarity

[ptheofan]

Summary

• render a compact download-profile pill on every individual download route
• connect downloads through their RR profile and download profile instead of bypassing the profile node
• highlight the complete connected route on pointer hover or keyboard focus
• incrementally reconcile keyed SVG nodes, edges, attributes, and text instead of rebuilding the live SVG on every poll
• match downloads to RR profiles by stable profile ID when available
• add a regression check for topology structure, keyed updates, and tracing hooks

Root cause

The topology collapsed each download profile into one shared node while drawing downloads directly from their RR profile. It also replaced the entire live SVG on every poll, resetting hover, focus, and animation state even when the same nodes still existed.

Impact

Every active download now visibly follows Put.io → RR profile → download profile → download. Existing keyed SVG elements retain their DOM identity and animations while changed text and geometry update in place; new elements are inserted and stale elements are removed.

Validation

• pnpm lint
• CI=true pnpm test — 118 tests pass
• CI=true pnpm test:coverage — 90.97% line coverage
• browser-verified SVG/node/path/text identity, text and progress updates, node insertion/removal, focus and hover preservation, and no restarted opacity animation

Fixes #55

[github-actions]

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Removed — this pull request is closed.