feat(detail): sticky minimized market header (binary + multi-outcome)

[dmnyc]

Summary

When you scroll into the comments section, the full-size market title is offscreen and you lose track of which market you're commenting on. Two parallel sticky-header components keep that context visible — one for binary markets, one for multi-outcome groups.

Components

• `StickyMarketHeader` (binary `Market`) — back arrow + truncated title + Yes / No percentage pills.
• `StickyGroupHeader` (multi-outcome `MarketGroup`) — back arrow + truncated group title + leading-outcome pill with its percentage + a `+N` badge for the remaining outcomes.

Both share identical chrome and positioning rules.

Implementation

• Lives inside the left grid column of each detail page so its width matches the column and the right-column trading / outcome panel stays unobstructed. A small negative right-margin (`lg:-mr-4`) reaches halfway into the 32px column gutter for a slightly less cramped feel.
• `.sticky-overlay-safe-top` utility — pins at `top: 0` and on macOS adds enough top padding to clear the 32px traffic-light / overlay strip, so the bar's translucent background fills the entire top of the frame (rather than leaving the macOS strip transparent). Padding is owned entirely by the class to avoid a shorthand-vs-longhand cascade fight with Tailwind's `py-*`.
• Always rendered, not conditional on scroll position. `position: sticky` needs a layout pass to compute its pin point and a freshly-mounted element above an already-scrolled viewport often fails to pin reliably. Keeping the bar in the layout always avoids the flicker / no-show edge case at the cost of a compact duplicate title between the H1 and the chart at the very top of the page.
• Background is `bg-slate-950/65` + `backdrop-blur` to match the rest of the app's sticky chrome (TopShell, settings drawer).

Also fixes a handful of UK spellings (`colour` → `color`, `minimised` → `minimized`) in nearby comments now that we're standardizing on US English.

Test plan

• Scroll into comments on the binary detail page — title + Yes/No pills stay pinned at top.
• Scroll into comments on a multi-outcome group page — title + leading outcome + `+N` stay pinned at top.
• On macOS, both bars' backgrounds extend up under the traffic lights without the title text falling behind them.
• Trading / outcome panel in the right column stays fully visible at every scroll position.
• Mobile / single-column layout — bars still pin correctly without the gutter overhang.
• biome check, tsc --noEmit pass.