Fix Profile Explorer state-loop + tooltip pin interaction; refresh global UX theme for a cleaner, professional UI

[Copilot]

This PR addresses two UI regressions (unstable tooltip pinning and Profile Explorer render-loop behavior) and updates the frontend visual system to a more professional, cohesive theme. Scope is intentionally narrow: fix functional breakpoints and restyle existing surfaces without changing page structure.

• UI behavior fixes

  • Profile Explorer: stops repeated null-state writes when probe rows are empty, preventing effect-driven re-render loops.
  • InfoTooltip: stabilizes hover-to-floating interaction and pin behavior (safePolygon + close delay + explicit pin handler), so users can reliably pin definitions.

• Test reliability for UI behavior

  • ProfileExplorer.test.tsx now mocks ECharts-based components to keep behavior assertions focused and avoid jsdom canvas/runtime noise in this unit test path.

• Theme + styling refresh (minimal churn)

  • Reworked design tokens in theme.css (ink/background/accent/surface/shadow/focus) for a cleaner, modern visual baseline.
  • Updated typography to Inter + JetBrains Mono.
  • Tuned active/hover/focus treatments and top-level shell/card geometry for a more polished, consistent feel.

• Type correctness

  • GuidedTourController now uses explicit Tour type import from shepherd.js to resolve TS namespace typing issues.

// ProfileExplorer: avoid no-op state churn when rows are empty
if (probeRows.length === 0) {
  if (selectedProbeCallIndex !== null) setSelectedProbeCallIndex(null);
  if (playbackCallIndex !== null) setPlaybackCallIndex(null);
  return;
}

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• scarf.sh
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