feat: api-reference primitives : TypeTable + ComponentPreview

[Shewart]

Summary

Ships the two API-reference primitives from the Phase 2 roadmap so consumers can hand-author prop tables and single-component demos without dropping into full razor:preview fences.

New components

<TypeTable> / <TypeRow> — the props/API reference table.

• Parent renders a four-column layout (Prop / Type / Default / Description) with type-code chips and a required badge.
• Children register into the parent via CascadingValue — same pattern as <CodeGroup> / <CodeTab>. Nothing rendered from <TypeRow> directly; it just hands its data up.
• Duplicates by Name are deduped silently.
• v1 is hand-authored; roadmap's v2 wires this up to XML-doc auto-generation via ShellDocs.Xml → <TypeTable Source="ShellUI.Button" />.

<ComponentPreview Component="..." ...props> — the declarative-prop cousin of razor:preview.

• Takes the target's registered tag name as a string Component prop; resolves it through the same TypeRegistry that backs razor:preview.
• Uses [Parameter(CaptureUnmatchedValues = true)] to receive arbitrary target-component props as attributes on the tag itself — no dictionary syntax, no fenced-block wrapper.
• Reflects on the target's [Parameter] types and coerces each string value via the shared SlotRenderer.Coerce (booleans, ints, enums, etc.).
• Renders live via DynamicComponent, plus a fumadocs-style stacked source-view (collapsed teaser + centered View source button, expands to show the reconstructed razor snippet with Copy and Hide). Source string is rebuilt from the resolved prop dict — attributes sorted alphabetically for stability, self-closing form when there's no body.
• Unknown Component renders an inline Unknown component: <code>Foo</code> error instead of throwing.

Infrastructure

• SlotRenderer.GetParameterProps and Coerce are now internal (were private) so ComponentPreview can drive the same per-type conversion its parent slot-renderer uses.
• ChildContentSource threading: when the target component declares a [Parameter] public string? ChildContentSource, SlotRenderer.BuildParameters now passes the raw child markup through unchanged alongside the usual ChildContent RenderFragment. That's what lets <ComponentPreview> reconstruct its source-view without asking the author to repeat themselves.

Fixes bundled in

• <Steps> rail centering. The border-left rail was drawn on the naked <ol>, and the number badge was pushed ~12px right of it — reading as "circle next to line" instead of "spine with beads on it". Whole list is now shifted right by 1rem so the border sits at global x = 1rem, and each badge is centered on that line via left: calc(-1rem - 0.5px). Badge fill changed from --muted → --card so it clearly breaks the rail (muted was the same tonal family as --border and blended into it). Badge bumped 1.85rem → 2rem, number 0.75rem → 0.8125rem.

Docs

• examples/ShellDocs.Preview/content/docs/components/type-table.md — Basic + Props sections
• examples/ShellDocs.Preview/content/docs/components/component-preview.md — Basic + self-closing examples, Props section
• meta.json sidebar updated: [..., "type-table", "component-preview"]