#530 [Bug Fix] HoverCard: let the card escape a clipping ancestor

Related issue

No existing issue — happy to open one if you'd prefer to track it there.

Description

HoverCardContent is position: absolute, so a positioned ancestor that hides its overflow — a scroll area, a table cell, a truncating container — clips the card instead of letting it overflow.

DropdownMenu already solves this: the root switches between is-absolute and is-fixed from options[:strategy], the content picks up its position through a group variant, and the controller passes the strategy on to computePosition. This gives HoverCard the same escape hatch, following that implementation exactly:

• HoverCard root gains group/hover-card plus is-absolute / is-fixed;
• HoverCardContent trades its hardcoded absolute for group-[.is-absolute]/hover-card:absolute group-[.is-fixed]/hover-card:fixed;
• the controller passes strategy: this.optionsValue.strategy || "absolute" to computePosition.

The default stays absolute, so existing usage renders and positions exactly as before.

Docs get an "Escaping a clipping ancestor" example, and mcp/data/registry.json is rebuilt (cd mcp && bundle exec rake mcp:build) so mcp-registry-check stays green.

Before	After

Testing instructions

1. cd gem && bundle exec rake — 292 runs, 0 failures; standardrb clean across 402 files.
2. cd docs && bin/dev, open /docs/hover_card and scroll to Escaping a clipping ancestor. Hover @joeldrapper: the card renders in full, overflowing the relative … overflow-hidden container around it.
3. Revert that example to the default strategy (drop option: {strategy: "fixed"}) and hover again: the card is clipped by the container — the behaviour on main today.
4. Every other HoverCard on the docs site still opens and positions as before, since the default is unchanged.

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Summary by cubic

Fixes HoverCardContent being clipped by ancestors with overflow: hidden. HoverCard now supports option: {strategy: "fixed"} to position the card against the viewport instead; the default remains absolute, so existing usage is unchanged.

• Mirrors DropdownMenu: the root switches between is-absolute and is-fixed, the content picks up its position through a group variant, and the controller passes the strategy to computePosition.
• Adds an "Escaping a clipping ancestor" docs example and rebuilds mcp/data/registry.json.
• Also fixes DropdownMenu's strategy ternary so unsupported values fall back to absolute like Floating UI, preventing a fixed card from drifting on scroll.