feat: Add skills management system with features extensibility layer

[mattbrailsford]

Summary

This PR introduces a comprehensive Skills Management System for Umbraco AI, built on a new Features extensibility layer for the provider/capability system. Skills are managed entities in Core that represent provider-backed AI operations (web search, code interpreter, image generation, etc.) that users can configure and assign to agents via a backoffice management UI.

Key Changes

Core Infrastructure (Features System)

• New feature marker interface (IAIFeature) enabling typed extension points on capabilities beyond the base capability contract
• Feature discovery methods on IAICapability and IAIConfiguredCapability: TryGetFeature<T>(), HasFeature<T>(), GetFeatures()
• Provider-level feature aggregation scanning all capabilities to expose available features
• Management API exposure of provider features in provider detail responses

Skills Domain & Persistence

• Skill domain model (AISkill) with properties: alias, name, description, skillTypeId, connectionId, settings, toolScopeIds, isActive, and standard audit metadata
• Skills feature interface (IAISkillsFeature) defining provider contract for skill type discovery and settings schema generation
• Skill descriptor (AISkillDescriptor) representing available skill types from providers
• Skill service (IAISkillService) for CRUD operations, availability queries, and schema resolution
• EF Core persistence layer with repository, entity factory, and migrations for both SQL Server and SQLite

Management API

• 8 REST endpoints for skill management:
  • GET /v1/skill — list all skills (paginated with filtering)
  • GET /v1/skill/{idOrAlias} — get skill detail
  • POST /v1/skill — create skill
  • PUT /v1/skill/{id} — update skill
  • DELETE /v1/skill/{id} — delete skill
  • GET /v1/skill/{alias}/exists — check alias uniqueness
  • GET /v1/skill/available-types — list available skill types (optionally filtered by connection)
  • GET /v1/skill/settings-schema — get dynamic settings schema for a skill type
• Request/response models with proper validation and immutability constraints (skillTypeId is immutable after creation)

Frontend UI

• Skills collection view with table listing skills, their types, connections, status, and modification dates
• Skills workspace editor with:
  • Details tab: connection picker, skill type selector, dynamic settings editor, tool scope picker
  • Info tab: version history, metadata, creation/modification timestamps
• Create flow with modal for selecting connection and skill type before editing
• Menu integration under the AI section alongside Connections and Profiles
• Type-safe models and data sources following Umbraco patterns

OpenAI Provider Integration

• OpenAI skills feature implementing IAISkillsFeature on the Chat capability
• Initial skill types: web-search, code-interpreter, image-generation with descriptors and optional settings schemas

Implementation Details

• Skills are provider-level entities (like connections), not agent-specific, enabling reuse across multiple agents
• Features are not metadata flags but full implementations with provider-specific logic and discovery
• Same patterns as capabilities — consistent API surface for feature discovery and access
• Settings are provider-specific — stored as JSON, schema-driven by providers for dynamic UI generation
• Tool scopes for permission grouping — allows agents to include/exclude skills via scope-based permissions
• Immutable skill type — prevents breaking changes to skill configuration after creation
• Optimistic concurrency via version tracking on save operations

Files Changed

• Core: 7 modified files (providers, configuration)
• Persistence: 3 modified files + 4 new files (entity, factory, repository, migrations)
• Web API: 1 modified file + 8 new controller files + 5 new model files + 1 mapping file
• Frontend: ~25 new files (constants, types, collection, workspace, repository, modals, manifests)
• OpenAI Provider: 1 new file (

https://claude.ai/code/session_015RD6irreUevTGNUnzEDZtD