feat(orderbook): add compact depth quantity labels

[jackhai9]

Prominent depth steps now show compact quantity hints inside the existing 132px chart overlay, so their approximate size is visible without taking more candlestick space. Labels use 11px text, a 16px height, and measured widths capped at 88px; long price bands display quantity alone. Each side shows at most two labels, with shared collision checks for labels, the current-price divider, and overlay controls.

Pixel rows sum actual level quantities for labels while preserving the original cumulative bar widths and complete price bands. Labels repaint and clear with the existing canvas. This releases orderbook userscript v2.7.207 and keeps the public installation URLs unchanged.

Validation:

• Full npm test: 1025/1025 passed; affected orderbook suite: 523/523 passed.
• Generated-artifact Playwright coverage: 3/3 compact-depth scenarios and 5/5 Unicode-symbol scenarios passed.
• Build, syntax checks, release contract, and git diff --check passed.
• Independent production and e2e reviews passed. Light and dark rendered screenshots were inspected using simulated market data and the actual generated script.
• Tampermonkey synchronization and post-reload live verification will be recorded separately after publication.