Add component category field to template manifest

[nick-pape]

Summary

The dev design says the template manifest should include "Component category (webpart, ACE, etc)". The current template.json schema (ISPFxTemplateJson) has no category field. This is needed for filtering, grouping, and display in the list-templates command.

Requirements

Schema addition

Add a category field to template.json:

{
  "name": "webpart-minimal",
  "description": "A minimal SPFx web part",
  "version": "1.0.0",
  "spfxVersion": "1.22.2",
  "category": "webpart"
}

Allowed categories

Category	Description	Templates
webpart	Web Parts	webpart-minimal, webpart-noframework, webpart-react
extension	Extensions	All extension-* templates
ace	Adaptive Card Extensions	All ace-* templates
library	Libraries	library

Behavior

• Field should be required in the schema
• Used by list-templates to group/filter output
• Could be used by create to show relevant templates based on user intent
• Validated by Zod schema in SPFxTemplateJsonFile

Implementation notes

• Update ISPFxTemplateJson interface in api/spfx-template-api/src/templating/SPFxTemplateJsonFile.ts
• Update Zod schema SPFxTemplateDefinitionSchema to include category as an enum
• Add category getter to SPFxTemplateJsonFile and SPFxTemplate
• Update all 18 template.json files to include the appropriate category
• Update toString() methods to display category

Acceptance criteria

• category field added to template.json schema
• All 18 templates have correct category values
• SPFxTemplate exposes category property
• Schema validation rejects invalid categories
• list-templates can group/filter by category