feat: add companion skills for business-analyst, implementation-planner, and implementation-executor agents

[anuragk16]

Summary

• Adds three Claude Code skills in claude/skills/ — one companion skill per agent (cc-business-analyst, cc-implementation-planner, cc-implementation-executor)
• Each skill guarantees its agent is always invoked (never bypassed inline) and creates a live task checklist in the terminal so progress is visible step by step
• Updates claude/README.md to document the new skills, add a "Available Skills" table, and extend the installation prompt to also copy skills into target projects
• Updates root README.md to list Claude Skills as a recipe category alongside Claude Agents

Changes

New: claude/skills/

• cc-business-analyst/SKILL.md — triggers business-analyst agent; tracks 5 steps: restate intent → identify ambiguities → refine document → validate criteria → flag open questions
• cc-implementation-planner/SKILL.md — triggers implementation-planner agent; tracks 4 steps: determine issue ID → explore codebase → create 4-hour plan → post to GitHub issue
• cc-implementation-executor/SKILL.md — triggers implementation-executor agent; tracks 6 steps: fetch plan → setup branch → implement tasks → push → create PR → assign & verify CI
• README.md for each skill with setup instructions and usage examples

Updated: claude/README.md

• Renamed to "Claude Agents & Skills"
• Added "Available Skills" table with skill–agent mapping
• Updated installation prompt (Step 1: agents with placeholder replacement, Step 2: skills copied as-is, Step 3: CLAUDE.md registration for both)

Updated: README.md

• Added Claude Skills row to the recipes table