REST API skills handlers

[JAORMX]

Description

Extend the basic REST API skill handlers (from #3744) with full OCI-backed operations. Adds request/response types, richer filtering, and delegates to the full SkillService from #3650.

Note: #3744 delivers the initial handlers with basic storage CRUD (list, get, install-record, uninstall). This task extends those handlers with OCI install, build, push, client/group filtering, and structured request/response types.

Dependencies: #3744 (basic API handlers), #3650 (full SkillService)
Blocks: #3652 (HTTP client), #3655 (ServerBuilder wiring + E2E)

Acceptance Criteria

• pkg/api/v1/skills.go handlers extended with full SkillService operations (builds on Skills API handlers #3744's basic CRUD)
• GET /api/v1beta/skills — adds client, group filtering (extends basic scope filter from Skills API handlers #3744)
• POST /api/v1beta/skills/install — installs from OCI reference via full service (extends metadata-only record from Skills API handlers #3744)
• POST /api/v1beta/skills/build — build OCI artifact (replaces "not implemented" from Skills API handlers #3744)
• POST /api/v1beta/skills/push — push to registry (replaces "not implemented" from Skills API handlers #3744)
• Request/response types in pkg/api/v1/skills_types.go
• Error handling with httperr.WithCode() (404 not found, 409 conflict for unmanaged, 422 validation errors)
• Unit tests for handlers, SPDX headers

Code Pointers

• pkg/api/v1/skills.go — basic handlers from Skills API handlers #3744 (to be extended)
• pkg/api/v1/groups.go — handler pattern reference
• pkg/api/v1/workload_types.go — request/response type conventions
• pkg/api/errors/handler.go — error handler wrapper

References

• Skill types, interfaces, and command/API stubs #3645, Skills API handlers #3744

[JAORMX]

Dependency update: This now builds on #3744 (basic API handlers for storage CRUD), which delivers working list, get, install-record, uninstall, and validate endpoints.

This task extends those handlers by adding:

• Full OCI-backed install/build/push operations (once Skill service implementation #3650 delivers the full service)
• Richer filtering (client, group)
• Request/response types in skills_types.go

Updated dependency chain: #3742 (basic service) → #3744 (basic API) → #3650 (full service) → #3651 (this: full API)

[JAORMX]

Deferring the group filter for GET /api/v1beta/skills to #3654. For #3651 I’m implementing only the client filter (plus existing scope) and keeping handler/type changes scoped to skills API + service list options. Group-based skill filtering will land alongside the group integration work.