refactor(cli): reorganize skill services

[codeaholicguy]

Summary

• Move CLI skill behavior from lib/util into a services/skill module with installer, registry, and index responsibilities.
• Route skill commands and setup/install/status flows through SkillService.
• Move skill selection UI into the command layer, consolidate registry discovery, and split skill/index tests.
• Add lifecycle docs for the refactor.

Validation

• npx tsc -p packages/cli/tsconfig.json --noEmit
• npm --workspace packages/cli test -- skill
• npm --workspace packages/cli test
• npm --workspace packages/cli run lint (passes with existing commands/channel.ts warning)
• npm run build
• npx ai-devkit@latest lint --feature skill-module-service-refactor
• pre-commit hook: secret scan, repo-wide lint, repo-wide tests

Risks

• Structural refactor with moved imports and tests; behavior intended to be preserved.
• Service layer still emits existing terminal UI progress messages; stricter UI/service separation is deferred.