feat: consumer DX : assembly scan, aliases, shelldocs add, inline-slot indent fix

[Shewart]

Summary

Bundles four consumer-DX wins into one branch. The pitch: get a ShellUI docs site from empty to authoring in one line of Program.cs and one CLI command.

1. Assembly-scan registration (ShellDocs.Components)

Kills the "hand-type RegisterComponent<T>() for every ShellUI component" tax:

builder.Services.AddShellDocs(o =>
{
    o.RegisterComponentsFromAssembly<ShellUI.Components.Button>();
    // every public ComponentBase subclass in the ShellUI assembly is now
    // referenceable from any razor:preview block or <ComponentPreview>.
});

New API on ShellDocsOptions:

• RegisterComponentsFromAssembly<TMarker>(Func<Type, bool>? filter = null) — scans the marker's assembly for public, concrete, non-generic ComponentBase subclasses and registers each. Handles ReflectionTypeLoadException gracefully.

• RegisterComponentsFromAssembly(Assembly, Func<Type, bool>? filter = null) — explicit form with a filter predicate:

  o.RegisterComponentsFromAssembly(typeof(ShellUI.Components.Button).Assembly,
      t => t.Namespace?.StartsWith("ShellUI.Components") == true);
  

• RegisterComponent(Type) — runtime overload alongside the existing generic form; validates ComponentBase assignability with a clear ArgumentException.

• [ShellDocsIgnore] attribute — opt-out marker for public components that shouldn't be reachable from markdown authoring.

Dogfooded on ourselves: AddShellDocs used to register each shipped primitive with an explicit thirteen-line block; now it's:

options.RegisterComponentsFromAssembly<Callout>(t => t.Namespace == "ShellDocs.Components.Content");

A new primitive dropped into Content/ auto-appears in the registry without editing ServiceCollectionExtensions.cs. MarkdownContent and PreviewFrame opt out via @attribute [ShellDocsIgnore].

2. Alias overloads (ShellDocs.Components)

For consumers who want a component registered under a different markdown-facing tag (e.g. <Btn> renders ShellUI.Button):

• RegisterComponent<T>(string tagName) and RegisterComponent(Type, string tagName) — writes to a new ComponentAliases dictionary on ShellDocsOptions.
• BuildTypeRegistry consults ComponentAliases before falling back to type.Name. Last-write-wins if the same type is registered under multiple aliases.
• Blank tag names rejected with ArgumentException.

3. shelldocs add <template> <name> CLI (ShellDocs.Templates + ShellDocs.CLI)

Scaffolds a starter .md page into content/. Three templates:

shelldocs add component MyBigCard
# -> content/docs/components/my-big-card.md
#    frontmatter + intro + razor:preview block + <TypeTable> skeleton + Notes

shelldocs add guide getting-started
# -> content/docs/guides/getting-started.md
#    frontmatter + intro + <Steps> skeleton + Next section

shelldocs add page faq
# -> content/docs/faq.md
#    blank frontmatter + H1

Slugifies PascalCase inputs (MyBigCard → my-big-card.md) and TitleCases kebab inputs (getting-started → "Getting Started"). Refuses to overwrite unless --force. Fails clean if no content/ directory is found.

PageTemplates static class in ShellDocs.Templates holds the three template bodies — same access pattern as the existing StarterPageTemplate. Program.cs's placeholder new command stub was repurposed into the wired-up add.

4. Inline-slot indent fix (ShellDocs.Markdown)

SlotExtractor.ReplaceComponentTags no longer .Trim()s the raw child content of inline component tags. The Trim was stripping the first line's indent and defeating SlotRenderer.Dedent — Markdig then re-interpreted the remaining 4-space-indented lines as an indented code block. Symptom was the same "literal <pre> around placeholder divs" bug that had already been fixed for razor:preview fences; the inline-tag code path was still hitting it. One-line change + prose comment explaining why.

5. TypeTable polish

• Required badge: text changed from required → Required; text-transform: uppercase and matching letter-spacing dropped; font-size bumped 0.68rem → 0.72rem to compensate for lowercase reading smaller
• Column headers: same treatment — dropped text-transform: uppercase + letter-spacing; font-size 0.75rem → 0.78rem. Headers now render as "Prop / Type / Default / Description" instead of "PROP / TYPE / DEFAULT / DESCRIPTION"

Roadmap updates

• Marked feat/content-primitives and feat/api-reference-primitives shipped with the actual delivered scope
• Added this branch (feat/consumer-registration-dx) as a shipped Phase 2 entry with the multi-package touch list
• Refined the Phase 2 milestone note — the primitive suite is complete; remaining Phase 2 work is feat/animation-polish and the 0.2.0-alpha NuGet cut

Test plan

• dotnet build shelldocs.slnx — clean, 0 warnings, 0 errors
• dotnet test shelldocs.slnx — 119 / 119 passing (+12 new: 8 AssemblyScanTests, 4 ComponentAliasTests, 8 AddCommandTests via reflection to match the existing InitCommandTests pattern; net new tests = 20 minus the 8 assembly-scan already counted in the last PR draft = 12)
• CLI smoke: dotnet run --project src/ShellDocs.CLI -- add component MyBigCard --dir <sandbox> writes content/docs/components/my-big-card.md with correct slug, PascalCase title, and template body
• Preview app: every primitive page (callout, card, steps, filetree, code-group, type-table, component-preview) renders with zero errors — proves neither the dogfooded assembly scan nor the SlotExtractor Trim fix regressed anything

New test coverage

AssemblyScanTests (8):

• Generic marker picks up concrete public components
• Skips abstract types
• Skips generic type definitions
• Skips non-ComponentBase types
• Respects [ShellDocsIgnore]
• Filter overload composes on top of system rules
• Registered types flow into TypeRegistry end-to-end
• RegisterComponent(Type) overload rejects non-ComponentBase

ComponentAliasTests (4):

• Generic alias overload registers under tag name (and short name no longer resolves)
• Type + tag alias overload registers under tag name
• Blank tag name rejected
• Last-alias-wins for repeated registration of the same type

AddCommandTests (8):

• component writes to content/docs/components/ with slugged filename
• guide writes to content/docs/guides/ with title-cased frontmatter title
• page writes to content/docs/ with blank body (no razor:preview)
• Unknown template returns non-zero
• Missing content/ dir returns non-zero
• Existing file without --force fails
• Existing file with --force overwrites
• Empty name returns non-zero