Create a consolidated README.md at the repository root.

Structure:

• Table of Contents
• Tools overview table with links to detailed docs
• Installation (consolidated for both tools)
• Getting Started
  • Configuration (jtk init, cfl init)
  • Authentication (API token generation)
  • Shared Credentials (ATLASSIAN_* env vars)
• Brief jtk overview → link to tools/jtk/README.md
• Brief cfl overview → link to tools/cfl/README.md
• Shell Completion
• Development (monorepo build commands)
• Contributing

Keep existing:

• tools/jtk/README.md - Full jtk command reference
• tools/cfl/README.md - Full cfl command reference

Estimated ~350 lines.