feat(traces): trace detail UX pass - #1485

🟢 Confidence 9/10 · safe to merge
Share attribution fuzzed against an independent union measure, and every caller of the reshaped strip/share API was read at the head.
_{quality 100/100 · no findings · tests partial · risk low}

Reworks the trace detail page: per-service time is now attributed to the innermost running span, plus a trace error callout, a start-time chip, self time/share in the span panel and a ?view= URL tab. Contained UI-only change; safe to merge.

• computeServiceShares sweeps self-intervals of the span tree instead of per-service unions
• collectTraceErrors replaces the two inline hasError copies and drives a new callout
• Anatomy strip takes rootSpans/spanCount plus a viewer-timezone start time
• $traceId keeps the view tab in ?view=

_{11b8afa · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}