feat: order flow, WebGL2 rendering, and extension points

[joeblau]

Summary

Adds the order-flow stack and a WebGL2 backend to @bloxwap/chart, and rebuilds the landing-page playground around them.

Refs #33, #34, #35, #36, #37, #38, #39, #40

Library

• Extension points (Extension points: custom series, panes, and pane primitives #33): series registry, host panes (stacked or docked) and pane primitives drawn behind or above the series.
• Depth (Depth data model + subscribeDepth datafeed channel #34): DepthBook model, a maintained L2 book manager (snapshot + diff deltas, sequence-gap resync, retry backoff) and the datafeed depth channel (pushDepth / subscribeDepth).
• Inline order book (Inline order book: depth histogram docked on the price axis #35): ladder or mirrored layout, docked or overlaid on the plot edge, 'up'/'down'/'side' theme tokens, vivid side-colored labels over a dim tint, bold best levels, per-row label culling, and an optional spread callback for the true spread when levels are aggregated.
• Liquidity heatmap (Liquidity heatmap (Bookmap-style) #36) with multi-stop color ramps and minOpacity.
• Trades, footprint, delta/CVD (Trade data model: tape, trade prints, and per-price volume #37, Footprint chart + delta/CVD #38) and the session volume profile / TPO pane (Session volume profile / TPO as a first-class pane #39).
• Visible-range volume profile (attachRangeProfile): round-price rows sized to the screen, mirrored up/down volume, POC outline, theme tokens, and tweened transitions on a frame scheduler.
• WebGL2 renderer (WebGL2 renderer backend #40): renderer: 'webgl2' with automatic Canvas2D fallback.
• chart.scale.scrollPrice(dy) and vertical plot panning while autoscale is off. Autoscale stays on by default, so drags keep the bars in frame.
• New range-profile and order-book icons.
• Fix: an onBook throw while the depth manager drains buffered deltas no longer strands the deltas behind it.

Playground / landing page

• Header controls move into the left rail (timeframe, chart type, indicators, Auto/%/Log). A right-edge disclosure picks the volume profile, the full order book, or none.
• The order book comes from Hyperliquid l2Book. Binance REST returns HTTP 451 from the US. The feed stitches two precisions for full depth and uses the bbo feed for the true spread.
• WebGL2 is on by default; ?renderer=canvas2d compares against Canvas2D.
• The mark-price, last-close and heatmap overlays are settings toggles, off by default.

Test plan

• npm run coverage: 1849 tests pass, 100% line/branch/function coverage on every file
• Landing page (docs dev server) checked in Chrome at 1m, 15m and 4h:
  • WebGL2 backend active; live Hyperliquid book (38 levels a side stitched); true spread label (Δ 1.0)
  • Right-edge disclosure switches profile / book / none; profile tweens on zoom
  • Rail controls work; autoscale holds while panning
• Spot-check light theme and a narrow (<600px) viewport

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