SkillService implementation and integration

[JAORMX]

Description

Phase 1 of the SkillService: implement basic storage CRUD operations and wire into the HTTP server. This delivers a working end-to-end stack (service + API) using the SQLite storage from #3648, without waiting for OCI library, installer, or client metadata.

The existing epic tasks (#3650, #3651, #3652, #3653) then extend this foundation with OCI operations, full validation, HTTP client layer, and CLI commands.

RFC: RFC-0041: SQLite-Based State Management
Dependencies: #3648
Blocks: #3650 (extends service), #3651 (extends API)

Scope — What This Delivers

• Basic SkillService implementation: CRUD against SkillStore (no OCI pull/push, no installer)
• Server wiring: createDefaultManagers() creates store + service, sqlite.Close() on shutdown
• Basic API handlers: list, get, install-record, uninstall endpoints backed by storage

Scope — What This Does NOT Deliver (handled by existing tasks)

• OCI pull/push → Skill service implementation #3650 (extends service with toolhive-core)
• Skill installer/extractor → Skill installer and extractor #3649
• Full API with validation/build/push endpoints → REST API skills handlers #3651 (extends API)
• HTTP client for CLI → Skills HTTP client for CLI #3652
• CLI commands → CLI skills commands implementation #3653
• Groups integration → Groups integration for skills #3654
• Final E2E wiring → ServerBuilder wiring and E2E tests #3655

Relationship to Existing Epic Tasks

#3648 (storage) → #3741 (this: basic service + API)
                      ├→ #3650 (extends service with OCI/installer)
                      └→ #3651 (extends API with full handlers)
                            └→ #3652 (HTTP client) → #3653 (CLI)

Code Pointers

• pkg/skills/service.go — SkillService interface
• pkg/storage/interfaces.go — SkillStore interface (from Skill state management #3648)
• pkg/api/v1/skills.go — existing 501 stubs
• pkg/api/server.go — ServerBuilder, createDefaultManagers(), shutdown path