Phase 1: Core CLI implementation

[gricha]

Summary

• Implement full Phase 1 of workout CLI as specified in SPEC.md
• 33 pre-populated exercises with aliases and muscle group tagging
• Zod schemas for type-safe data validation
• JSON file storage in ~/.workout/

Commands

• workout exercises list/show/add/edit/delete - Manage exercise library
• workout templates list/show/create/delete - Manage workout templates
• workout start/log/status/done/cancel - Workout session flow
• workout history <exercise> - Exercise progression history
• workout last - Last workout summary

Infrastructure

• AGENTS.md with skills (validate, test, create-pr, release)
• GitHub Actions CI + release workflow with cross-platform binaries
• install.sh for curl-pipe installation
• 79 tests covering types, storage, business logic, and CLI integration

Test Plan

• bun run validate passes (lint, format, typecheck, 79 tests, build)
• CLI tested end-to-end in test/cli.test.ts