refactor(inspect): polish pass

[ivanrdvc]

Summary

• Per-trace raw spans toggle (hover-revealed {} on root rows, sticky when on) replacing the global flag; toolbar {} kept as bulk on/off across all traces. State centralized in useRawRoots.
• Span tree row redesign: flat colored kind label (no Badge border), hairline rails, small filled leaf dot, errored rows get a 2px left strip, tokens render as ↑in ↓out.
• Perf: SpanTreeRow memoized with content equality + stable callbacks so unaffected rows skip re-render on toggle.
• Bundled with earlier polish on this branch: breakdowns + JSON display fixes, truncated-attr enrichment seam, shared Spinner, formatPercent adoption.

Test plan

• Large session: flip toolbar {} (all traces) and a per-trace {} — verify smoothness.
• Errored span: confirm 2px left strip on the row and no inline "error" pill.
• Chat span: token cell renders ↑1166 ↓50 with cached/ctx delta still visible.
• URL ?span=<infraId>: the trace's raw should auto-flip on so the span is reachable in the tree.
• Conversation tab, palette, refresh, auto-refresh: nothing regressed in drawer, sessions, traces routes.