distribution: redesign as percentile whisker with landmark axis

[Flotapponnier]

Full rewrite of the distribution chart to address the "I click and other things appear/disappear, I can't read this" feedback.

What changed

1. Whisker shape per row — one continuous shape replaces the old 3-marker + band + median-guide combo: connector → p50 dot → thick p50→p90 bar → thinner p90→p99 tail → p99 wall. Silhouette encodes the spread story in one eye-jump; tooltip combines all three numbers in a single Hint.

2. Landmark axis above the rows — X axis snaps to power-of-10 decades formatted via `fmtUnit` (e.g. `100ms · 1s · 10s · 1min · 10min · 1h`). Tick labels live in a header rail above the rows and faint gridlines repeat per row, so the reader can decode any whisker's position back to a real value without hovering.

3. No more "shifting world" on exclude — toggling a provider rarely changes the visible landmarks (the floor / ceiling only move when data crosses a decade boundary). When they do move, the transition runs through the shared `useAnimatedDomain` hook (450 ms ease-out, 20 % significance threshold — same easing as the time-series chart's Y-axis re-zoom).

4. Excluded rows dim in place — the row keeps its grid slot and its rank #N. No reflow, no rank renumbering. Click anywhere on the row to re-include. A "Reset · N excluded" button appears in the header when any provider is hidden.

5. Stable rank column — `drop journal framing #1..#N` on the left, derived from the unchanging sort order. Lets the reader anchor on a row even when the row is dimmed.

Refactor

• Extracted `useAnimatedDomain` from `time-series-chart.tsx` to `src/hooks/use-animated-domain.ts` so both charts share the same easing.
• `time-series-chart.tsx` now imports the hook (no behavior change).
• New helper `pickLandmarks(min, max, unit)` picks power-of-10 decade ticks. Works for every unit OCB uses (`ms`, `s`, `slots`, `count`, `bps`, `pct`, `usd`) via `fmtUnit` formatting — no per-unit lookup table.

Removed

• The old 50 % median guide (was a pixel midpoint, meaningless on log scale).
• The footer `min … max` text (replaced by labelled ticks above).
• The 3-icon `` (replaced by a single whisker-shape legend that mirrors what the eye actually sees).